Soils of the Right Bank of the Nogoa River

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SoilsSoils ofof thethe RightRight BankBank ofof thethe NogoaNogoa RiverRiver EmeraldEmerald IIrrigationrrigation Area,Area, QueenslandQueensland

RJ Tucker, SA Irvine, MD Godwin and RC McDonald 276 Land Resources Bulletin

SOILS OF THE RIGHT BANK OF THE NOGOA RIVER,

EMERALD IRRIGATION AREA, QUEENSLAND.

VOLUME ONE

RJ Tucker1, SA Irvine2, MD Godwin3 and RC McDonald1

Department of Natural Resources and Mines, Queensland Brisbane 2003

1 Formerly Queensland Department of Primary Industries, Land Resources Branch 2. Department of Natural Resources and Mines, Queensland 3. Environment Protection Agency, National Parks and Wildlife Service, formerly Queensland Department of Primary Industries Agricultural Chemistry Branch ii

QNRM03091 Volume One ISSN 1327-5763

This publication was prepared by officers of the Department of Natural Resources and Mines. It may be distributed to other interested individuals and organisations.

This report is intended to provide information only on the subject under review. There are limitations inherent in land resource studies, such as accuracy in relation to map scale and assumptions regarding socio–economic factors for land evaluation. Readers are advised against relying solely on the information contained herein. Before acting on the information conveyed in this report, readers should be satisfied they have received adequate information and advice specific to their inquiry.

While all care has been taken in the preparation of this report, neither the Department of Natural Resources and Mines nor its officers or staff accepts any responsibility for any loss or damage that may result from any inaccuracy or omission in the information contained herein.

Department of Natural Resources and Mines Locked Bag 40 Coorparoo DC Qld 4151 iii

CONTENTS

List of figures iv List of tables v Acknowledgements v

1.0 Introduction 1 1.1 Background 1 1.2 Purpose and extent of survey 2

2.0 Survey Method 3

3.0 Climate 5 3.1 Rainfall 5 3.2 Temperature, sunshine and cloud 6 3.3 Humidity 9 3.4 Evaporation 9 3.5 Drought 10

4.0 Geology And Landform 11 4.1 Geology 11 4.2 Landform 11 4.3 Landscape units 11 4.4 Geomorphology 22

5.0 Hydrology 13 5.1 Surface hydrology 14 5.2 Sub-surface hydrology 14

6.0 Natural Vegetation 18

7.0 Soils 22 7.1 Unique map areas 25 7.2 Morphology and classification 28 7.3 Chemical and physical attributes 28

8.0 Land Use 62 8.1 Land use prior to irrigation development 57 8.2 Land use after irrigation development 57

9.0 References 58

List of Figures

Figure 1. Locality plan 1 Figure 2. An example of a soil type code used in this report 3 Figure 3. Mean monthly rainfall and probabilities at Emerald Airport 7 Figure 4. Mean daily maximum and minimum temperatures for each month at Emerald 7 Figure 5. Mean monthly relative humidities at Emerald Post Office 9 Figure 6 Mean daily evaporation per month from class A pan evaporimeter at Emerald Post Post Office from 1968 to 1979 9 Figure 7. Diagrammatic landscape section showing the relative positions of landscape units on the Left and right banks of the Nogoa River 12 Figure 8. Location of observation bores in the EIA right bank. 15 Figure 9. Mean pH for the cracking clays 31 Figure 10. Mean pH for the alluvial duplex soils 31 Figure 11. Mean pH for the Tertiary sediment duplex soils 31 Figure 12. Mean pH for the miscellaneous soils 31 Figure 13. Mean EC for the cracking clays 33 Figure 14. Mean EC for the alluvial duplex soils 33 Figure 15. Mean EC for the Tertiary sediment duplex soils 33 Figure 16. Mean EC for the miscellaneous soils 33 Figure 17. Mean chloride levels for the cracking clays 34 Figure 18. Mean chloride levels for the alluvial duplex soils 34 Figure 19. Mean chloride levels for the Tertiary sediment duplex soils 34 Figure 20. Mean chloride levels for the miscellaneous soils 34 Figure 21. Mean ESP for the cracking clays 38 Figure 22. Mean ESP for the alluvial duplex soils 38 Figure 23. Mean ESP for the Tertiary sediment duplex soils 39 Figure 24. Mean ESP for the miscellaneous soils 39

Figure 25. Relationship between ESP and EC1:5 39 Figure 26. Relationship between CEC and clay percentage 41 Figure 27. Mean CEC for the cracking clays 42 Figure 28. Mean CEC for the alluvial duplex soils 42 Figure 29. Mean CEC for the Tertiary sediment duplex soils 42 Figure 30. Mean CEC for the miscellaneous soils 42 Figure 31. Mean Ca:Mg for the cracking clays 43 Figure 32. Mean Ca:Mg for the alluvial duplex soils 43 Figure 33. Mean Ca:Mg for the Tertiary sediment duplex soils 43 Figure 34. Mean Ca:Mg for the miscellaneous soils 43 Figure 35. Mean CAR for the cracking clays 44 Figure 36. Mean CAR for the alluvial duplex soils 44 v

Figure 37. Mean CAR for the Tertiary sediment duplex soils 44 Figure 38. Mean CAR for the miscellaneous soils 44 Figure 39. Mean clay percentage for the cracking clays 48 Figure 40. Mean clay percentage for the alluvial duplex soils 48 Figure 41. Mean clay percentage for the Tertiary sediment duplex soils 48 Figure 42. Mean clay percentage for the miscellaneous soils 48 Figure 43. Mean sand percentage for the alluvial duplex soils 49 Figure 44. Mean sand percentage for the Tertiary sediment duplex soils 49 Figure 45. Mean total phosphorus for the cracking clays 52 Figure 46. Mean total phosphorus for the alluvial duplex soils 52 Figure 47. Mean total phosphorus for the Tertiary sediment duplex soils 52 Figure 48. Mean total phosphorus for the miscellaneous soils 52 Figure 49. Mean total potassium for the cracking clays 53 Figure 50. Mean total potassium for the alluvial duplex soils 53 Figure 51. Mean total potassium for the Tertiary sediment duplex soils 53 Figure 52. Mean total potassium for the miscellaneous soils 53 Figure 53. Mean total sulfur for the cracking clays 55 Figure 54. Mean total sulfur for the alluvial duplex soils 55 Figure 55. Mean total sulfur for the Tertiary sediment duplex soils 55 Figure 56. Mean total sulfur for the miscellaneous soils 55

List of Tables

Table 1. Coefficients of spatial variation (CV) of mean rainfall from September 1975 to March 1976 for four sites in the Emerald Irrigation Area. 6 Table 2. Rainfall intensity for different durations and estimates for return periods, Emerald. 6 Table 3. Temperature after irrigation of BUg-2 soil 7 Table 4. Diurnal temperature ranges of (BUg) soil at four depths at Capella 8 Table 5. Average number of days of frost at Emerald Airport 8 Table 6. Average morning and afternoon cloudiness for Emerald 8 Table 7. Number of recorded droughts, Emerald Airport 10 Table 8. Location and depths of groundwater investigation bores of the Geological Survey of Queensland on the Right bank, Emerald Irrigation Area, 1979 15 Table 9. Location, elevation, depth of bore and water levels in QWRC observation bores 17 Table 10. Dominant and minor soil types of the mapping units 25 Table 11. Laboratory analysis conducted on soils in the study area 29 Table 12. Groups, subgroups and number of profiles analysed 30 Table 13. Analysed soil types with subsoil pH 5.5 or less 32

Table 14. Weighted root zone salinity (ECse) of the analysed soils 36 Table 15. Depth to weighted root zone salinity thresholds of the analysed soils 37 Table 16. Depth to sodic and strongly sodic layers in the soils analysed. 39 vi

Table 17. Relationship of clay activity ratio in relation to clay mineralogy 43 Table 18. Effective rooting depths and plant available water capacity of the soils analysed 37 Table 19. Mean dispersion ratios for soil groups. 47 Table 20. Average silt percentages for the analysed soils. 50 Table 21. Mean surface fertility data (0-0.1 m depth) 51

vii

Acknowledgements

The authors wish to thank various people for their assistance during the preparation of the report, in particular: • Bruce Forster for peer review, constructive criticism and editing of the final report; • Terry Donnollan and Val Eldershaw for editing; • Jeff Lloyd for his valuable contribution to the groundwater interpretation; and • Diane Bray for cover design and publication of report.

Accompanying map (in back pocket of report)

P 1820 Soils of Emerald Irrigation Area Right Bank (1: 25 000)

APPENDICES (Volume 2)

The appendix sections are presented in the report entitled (QNRM03019 Volume 2 – Appendices and are recorded on the CD accompanying this report.

1. Detailed descriptions of the mapping units 1

2. General ratings used for interpretation of soil chemical analyses 112

3. Morphological and analytical data for representative profiles of selected soil types 113

4. Plant species found on the Right Bank of the Emerald Irrigation Area 219

viii

1.0 INTRODUCTION

1.1 Background

The Emerald Irrigation Area (EIA) is located on both sides of the Nogoa River adjacent to the town of Emerald. The right bank section, the focus of this soil survey, is situated east and north-east of Emerald, with the Nogoa River forming the northern boundary. Immediately north and west of the study area is the left bank soil survey area (McDonald and Baker, 1986).

Figure 1. Locality plan

Water for irrigation is supplied from the Fairbairn Dam, 19 km upstream of Emerald on the Nogoa River. The dam has a storage capacity of 1 301 000 ML. The safe annual yield of the facility is 147 000 ML, about 10% of the storage capacity. Within this storage, 121 200 ML is available for release for irrigation. Water is supplied to the irrigation area via the Selma Main Channel for the Left Bank section, and Weemah Main Channel for the Right Bank section. Riparian farms are supplied from water released into the Nogoa River, and some supplies are pumped to farms directly from Lake Maraboon, the dam storage. Prior to the building of Fairbairn Dam, other storages (the Selma, Town and McCosker weirs) were the only water storages on the Nogoa River. Selma Weir supplied water to research farms and supplemented urban supplies from Town Weir.

McCosker Weir supplied irrigation water, but has been breached for many years and now ponds little water. Other minor weirs were installed following coal mining developments to service new developments and other water users.

The main objectives of the Emerald Irrigation Scheme according to the Department of Primary Industries and Irrigation and Water Supply Commission (1966) were: • to improve overall growth in the district; • increase and stabilise rural production, provide fodder for drought mitigation and supplementary feeding of stock; and • to increase population and business activity in Central Queensland generally.

When the objectives were defined, Central Queensland’s population had grown much more slowly over the preceding 20 years compared to northern and southern Queensland. Since then, substantial areas of land have been developed for agriculture, and many coal mines have been developed. Emerald has become an important regional centre. Water from Fairbairn Dam is used for irrigation, urban supplies and coal mine operations. Irrigated cropping has concentrated on high value crops such as cotton and horticultural crops.

Gunn (1967a) and Story (1967) have briefly summarised the early history of the general area, respectively quoting Rogers (1960) and information prepared for the Springsure Centenary (Anon 1959). Previous soils information on the area included 1:2 000 000 soil association mapping (Isbell et al. 1967), 1:1 000 000 soil association mapping (Isbell and Hubble 1967), 1:506 880 land system mapping (Story et al. 1967), and 1:126 720 soil mapping (McDonald 1970). Isbell (1962) described soils of the brigalow lands, Gunn (1966) described sites sampled for land system mapping and Gunn (1974, 1976b) described soil catenas on denuded laterite profiles and weathered basalt in Central Queensland. Gunn and Nix (1977) collated land systems of Central Queensland into land units. McDonald et al. (1984) documented the cracking clays soils in the Emerald Irrigation Area. In addition, a number of soil mapping projects have been conducted adjacent to the study area (McDonald and Williams 1985, McDonald and Baker 1986, McCarroll 1998 and Irvine 1998).

1.2 Purpose and extent of survey

McDonald (1970) identified principal areas of soils suited to irrigation development in the EIA. Development was subsequently approved for soils on both banks of the Nogoa River. This soil survey of the right bank section was undertaken after a similar survey of the left bank section (McDonald and Baker 1986). The right bank survey, a high intensity survey with a publication scale of 1:25 000, was conducted from 1972 to 1979. A soils map and land suitability information for irrigation development and farm subdivision were provided directly to the Queensland Water Resources Commission, the developing authority at the time.

The survey area of 15,030 ha lies on the right bank of the Nogoa River (looking downstream), extending from 6.5 km south of Emerald to 24 km north-east of Emerald. Weemah Main Channel, then Winton Creek form the southern and south-eastern boundaries of the survey area. Based on the soils mapping, fifteen farms, varying in area from 214 to 334 ha, were designed by the Queensland Water Resources Commission and serviced by the Weemah channel. Other areas are served by pumping from the river. Subsequent mapping of 600 ha for irrigation suitability was reported in McDonald and Williams (1985).

2.0 SURVEY METHOD

Mapping was carried out for a publication scale of 1:25 000. The legend-making phase of the soil survey consisted of several collections of data. Initially soils were described every 320 m (16 chains) along traverses on a 3.2 km (2 mile) grid. From these data, a preliminary working legend was prepared.

Early mapping was carried out using 1:15 840 scale monochrome enlargements of colour aerial photography flown in 1969. Subsequently, descriptions were made in representative photographic patterns over the survey area. Photographic patterns were selected using 1:7920 enlargements of the colour aerial photos. The legend was revised. At this point, the alluvial plains were divided into landscape units 1A and 6A. The legend was revised once more during the mapping. The 1:7920 colour prints were used as field sheets. Having been flown at the end of a drought, the colour air photography showed soil colours and patterns very well. Field inspections were conducted along traverse lines. The traverses were based on grid lines used for QWRC contour survey and which were constructed within a mile square grid. The lines were 91.4 m (100 yards) apart. At the northern and eastern edges of each square mile, the last grid line was only 55 m (60 yards) from the next grid line.

Soils were described at intervals along the traverse lines using either a 7.5 cm Jarret hand- auger or 5 cm-diameter soils tube. Depth of examination was usually 1.5 m, or to rock or gravel layers shallower than 1.5 m. Observations varied from one per hectare to less than one per sixty hectares depending on soil variability. At each site, descriptions were made of vegetation, microrelief, depths of horizons and their colour, texture, pedality and inclusions. Field pH was usually described every 0.3 m down the profile. Where possible, structure was also described. Other significant soil attributes were described such as drainage, gravel and cracks when present. Landforms and many general site details were often not described because of the high intensity of the survey and the fact that they could also be determined directly from the aerial photography.

The soils were mapped based on soil morphology and pH trend. Soil types were identified by an alpha-numeric code derived from the landscape unit; the subdivision of the primary profile form given by Northcote (1979); and a number, where there were more than one soil type of the same primary profile form with a landscape unit. An example is given in Figure 2. Number indicates that this is Soil Type Name : 6AUg-10 the tenth soil type of clay soils in landscape unit 6A

Landscape Unit Subdivision of the primary profile form (Northcote 1979) Here it means uniform texture profile (U) and clay cracks seasonally (g)

Figure 2. An example of a soil type code used in this report

In the case of deeply gilgaied cracking clays soil types an extra letter ‘g’ was added to the soil name, for example 6AUgg, TsUgg-1. Soil types in landscape units 1A, 3A and B do not end with sequential numbers, because soil types in these landscape units do not occur on the right bank. These soil types are only represented on the Left Bank (McDonald and Baker 1986).

Boundaries between soils were mapped on colour aerial photography, and then drafted onto a QWRC base plan. The soils map was printed in 1980. Representative soil types were sampled for laboratory analysis. Samples and descriptions were taken from cores extracted by a Proline drilling rig, or soil tubes. The samples were analysed by Agricultural Chemistry Branch DPI at Indooroopilly. Data from sites, previously described and analysed (Shaw and Yule 1978; Shaw, unpublished data), have also been used in this study.

2.1 Soil type definition

The term ‘soil type’ replaces the term ‘soil profile class’ previously used as the basic soil taxonomic unit. The soil types are made up from records of individual soil profiles, described during the survey. The profiles have similar morphological characteristics and trends in pH down the profile. In this survey, the soil type is independent of scale and variability. The descriptions of all soil types are not equally precise. In some cases, variability within the soil type will be small, and a profile in one area will closely resemble a profile from another. In another soil type, horizons or horizon widths may vary considerably, as may attributes within the horizons; examples of the contrasts are BUg-2, which has low variability, and TsGn-5, which is highly variable.

To map the soils to a consistent level of variability would have resulted in additional soil types and been impracticable, requiring much more closely spaced observations in areas of high variability. As well, a much larger scale of mapping would have been required in order to demonstrate the resulting increase in precision. All this would have gone well beyond the scope of the purpose of this study.

2.2 Mapping units definition

Mapping units (Beckett and Webster 1971) were named after the dominant soil type found in each unit. Other soils, or unusual ranges in the dominant soil type, which could not be mapped separately are also contained within the mapping unit. Mapping units contain >70% of the dominant soil type. Where contrasting soils regularly occurred together with sufficient frequency (approximately >30%), compound mapping units were created, with the dominant soil named first. Each occurrence of a mapping unit has a unique combination of landform and soils, and is referred to as a unique mapping area (UMA) (after Basinski 1978). UMA’s with similar names will vary slightly from one unit to another in purity and the nature of the minor soil types present. In some cases, the full range of properties of the main soil type will not be found within individual units. One UMA may exhibit properties consistent with one end of the range found in the soil type while another map unit may have properties at the other end of the range.

The map reference is based on the landscape units and soil types. Eroded and gullied phases have been included, as well as miscellaneous units, which include rock outcrop, or cobbly or stony land. On the map, mapping units have been coloured according to whichever soil type is dominant. The compound map units are not included in the map reference.

3.0 CLIMATE

The climate of the area is sub-humid to semi-arid, subtropical. Major climatic characteristics are: • strong summer dominance of rainfall; • relatively high incidence of high intensity rainfall in summer; • high variability and low reliability of rainfall; and • hot summers and mild winters with warm days and cool to cold nights.

Climatic data for the area are described by the Australian Bureau of Meteorology (1965, 1975a,b), Fitzpatrick (1967a,b), Robinson and Mawson (1975), Hammer and Rosenthal (1978), Rosenthal and Hammer (1979) and Clewett et al. (1999). Data presented have been taken from these sources or were obtained from the Australian Bureau of Meteorology.

3.1 Rainfall

The average annual rainfall is 639 mm. Rainfall is strongly seasonal with 73% falling in the summer months October to March (Figure 3). The four wettest months, December to March, account for 58% of the rainfall. The mean monthly rainfall and 20%, 50% and 80% probability rainfall curves are shown in Figure 3. Occasional very high falls give an exaggerated impression of the most commonly occurring rainfall (compare mean monthly rainfall with 50% probability). Occasional higher falls are most likely to occur in January to February (20% probability compared with mean). The average number of rain days per year is 59.5, of which 40 occur in summer.

Mean 200 20% probability 175 50% probability 150 )

m) 80% probability 125 100

ainfall (m 75 R 50 25 0 JASONDJFMAMJ Month Figure 3. Mean monthly rainfall and probabilities at Emerald Airport (Clewett et al. 1999)

Rainfall from thunderstorms is important (Australian Bureau of Meteorology 1965), particularly regarding its relevance to soil erosion. Thunderstorms are most frequent in December (Prentice et al. 1965) and have very low frequency from March to September inclusive. Between 70% to 80% of the monthly totals from September to December result from thunderstorms. Large thunderstorms provide useful rainfall over a width of 8-16 km along a 64 km path. Consequently, rainfall distribution is quite variable at that time of the year, which is supported by recordings from rain gauges at four widely separated trial sites in the EIA from September 1975 to March 1976 (Table 1).

Table 1. Coefficients of spatial variation (CV) of mean rainfall from September 1975 to March 1976 for four sites in the Emerald Irrigation Area. Period CV% September – December 1975 20 (Thunderstorm season) January – March 1976 5

Higher variability of early summer rainfall has been observed to continue through the whole summer period if general rainfall is low. Data on rainfall variability for mean and six monthly recordings at Emerald are given in Fitzpatrick (1976). Coefficients of variation over time are: • annual rainfall 37%; • summer (November to April) 38%; and • winter (May to October) 62%.

High rainfall intensities, resulting in high runoff rates and potentially severe erosion, are most common in the months, October to December. Rainfall intensity for different durations and estimated return periods are given in Table 2.

Table 2. Rainfall intensity for different durations and estimates for return periods, Emerald. Return period Rainfall intensity (mm/hr) for various time intervals (years) 6 min 30 min 1 hr 3 hrs 6 hrs 1 98.3 48.2 31.7 14.2 8.6 10 169.7 83.2 54.7 24.5 14.9 100 235.5 115.5 76.0 33.9 20.7 Source: Australian Bureau of Meteorology

Data from Fitzpatrick (1967b) for nearby locations suggests that about 90% of rain days in summer have rainfall < 50 mm. In summer, rainfall normally occurs within 5 consecutive rain days. In winter and until December, rainfall events last up to 2 to 3 days, or as isolated occurrences (Fitzpatrick 1967b).

3.2 Temperature

Air temperature Mean daily maximum and minimum temperatures for each month are shown in Figure 4. December is the hottest month with mean maximum and minimum temperatures of 34.7oC and 20.8oC and July the coldest with corresponding temperatures of 22.6oC and 7.1oC. Temperatures in excess of 38oC occur, on average, on 19 days a year. January (seven days) and December (five) have the highest incidence with other summer months having relatively few (November, three; February, two; October and March, one each). Rosenthal and Hammer (1979) provide probability tables of heatwave dates, occurrence and duration of heatwaves and weekly mean maximum temperatures. Skerman (1958) has reported that three consecutive days over 38oC adversely affect grain sorghum crops; Rosenthal and Hammer (1979) attribute this to the death of flowers still enclosed in the panicle.

40 Maximum 35 Minimum 30 25 20 15

Temperature (C) 10 5 0 JASONDJFMAMJ Month

Figure 4. Mean daily maximum and minimum temperatures for each month at Emerald (Clewett et al. 1999)

Soil temperature Limited data are available on soil temperatures, as these have not been recorded in the EIA. However, some observations can be reported. Data collected on the BUg-2 soil by MN Hunter (pers. comm.) showed that very high temperatures could occur in summer.

In one observation, dry soil had a temperature at the surface of 50.0oC and upon wetting with water at 32.8oC, the soil temperature rose by 10.6o to 60.6oC. This temperature began to fall after 3 minutes. Rise in temperature after wetting depends on clay content, clay type and initial moisture content. BUg-2 soil has a high content of very active clay types, and the soil was most likely quite dry before irrigation, which explains the considerable heat flux. Repeated observations in pots showed temperature rises of 3.4oC to 6.6oC. Note that these temperature increases are very short term. In another observation, soybean seedlings were affected during a heatwave. Soil temperatures recorded at various depths after irrigation in the EIA are shown in Figure 3.

Table 3. Soil temperature at three depths after irrigation of BUg-2 soil Soil depth (m) Soil temperature (oC) 18 Dec 19721 27 Dec 19722 0.01 54.9 56.0 0.05 36.4 39.8 0.10 29.7 34.7 1 2 days after furrow irrigation 2 11 days after furrow irrigation Source: MN Hunter (pers. comm.)

Similar results were found with soil temperatures recorded in related soils near Capella, 50 km north of Emerald (MM Sallaway, unpublished data). Examples are shown in Table 4. Soil temperature at 0.5 m depth on bare BUg-2 at Emerald varies with monthly means of 31.4oC to 33.9oC in December to February and 16.0oC to 16.7oC in June to July (G. Murtha, unpublished data).

Table 4. Diurnal soil temperature ranges at four depths of BUg soil at Capella o Soil depth (m) Diurnal temperature ranges ( C) 17-21 Aug 1984 sunflower 20-24 Mar 1984 fallow 0.01 7-11 to 37-39 21-22 to 48-49 0.05 N/A 23-24 to 31-34 0.10 15-16 to 21-22 26 to 29 0.40 18 to 19 27 to 28

Frost Information on frost has been provided by Clewett et al. (1999). Frost has been measured by the number of days where temperatures fall below 2.2oC and subdivided into light (between 0 oC and 2.2oC) and heavy (less than 0oC). Frosts are infrequent, even in winter, as shown in Table 5.

Table 5. Average number of days of frost at Emerald Airport Average number of days during winter Frost type June July August Light (0 to 2.2oC) 1 3 1 Heavy (<0oC) 0 1 0 Source: Clewett et al. 1999

According to Bourne and Tuck (1993) the frequency and severity of frosts vary considerably from one locality to another, due to differences in relief. It is expected that frost incidence and severity will increase in lower lying areas such as drainage lines and lower slopes. Light frosts have occurred as early as 23 April and as late as 4 November, but a 50% probability occurs from 10 June to 17 August. Heavy frosts have been recorded as early as 29 April and as late as 9 September, however, a 50% probability occurs from 8-26 July (Hammer and Rosenthal 1978).

3.3 Radiation

Sunshine and cloud cover Maps of sunshine hours prepared by the Australian Bureau of Meteorology (1975) show sunshine hours every third month. The average daily duration of sunshine is at a maximum in October (approx. 9-10 hrs); it decreases to a minimum in January (approx. 7-8 hrs); April and July have approximately 8-9 hrs of sunshine per day. The annual average is 8-9 hrs per day. Cloud cover reaches a maximum in mid summer (December to February) and a minimum in early spring (August to September). Note that the maxima for 9am and 3pm readings in mid summer are in different months as shown in Table 6.

Table 6. Average morning and afternoon cloudiness for Emerald Time Average cloudiness, tenths July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June 9 am 2.5 2.1 2.4 3.0 3.8 4.3 4.6 3.9 3.9 2.8 2.5 3.3 3 pm 3.0 2.6 2.7 3.3 4.1 4.8 5.4 5.7 4.7 3.9 3.6 3.8 Source: Australian Bureau of Meteorology, 1975b

3.4 Humidity

Humidity peaks in summer in February and again in May, with a slight trough in April and a pronounced trough in September to November (see Figure 5). Average relative humidity at 9am peaks in winter and is lowest in spring and early summer.

9am mean relative humidity

80 3pm mean relative humidity 70 ) 60 50 40 30

ealtive Humidity (% Humidity ealtive 20 R 10 0 JASONDJFMAMJ Month

Figure 5. Mean monthly relative humidities at Emerald Post Office

3.5 Evaporation

Evaporation figures from a class A pan evaporimeter are shown in Figure 6 for the twelve years 1968 to 1979. The period November to December has the highest evaporation and June to July the lowest.

mean monthly evaporation 12 yearly average 10

4 Evaporation (mm) Evaporation 2

0 JASONDJFMAMJ Month

Figure 6. Mean daily evaporation per month from class A pan evaporimeter at Emerald Post Office from 1968 to 1979

The mean annual evaporation is 2147 mm although it can vary from 1645 mm in a drought year such as 1969, to 2700 mm in a wet year like 1974.

3.6 Drought

According to Bourne and Tuck (1993), a drought, which is a normal feature of the area, is defined as an occasion when climatic variations are so severe, that the risks (in terms of agricultural returns) greatly exceed what would be considered to be an acceptable level of commercial risk. Dry periods usually occur every winter (Figure 3). The length of the dry period is determined by the arrival of spring storms (Bourne and Tuck, 1993). Droughts can be defined by the duration of the dry period. According to Clewett et al. (1999), there are three drought categories: • Seasonal - 6 months duration; • Major - 12 months duration; and • Extended - 24 months duration.

The number of droughts and their respective category are shown in Table 7. Major droughts have occurred in 18% of recorded years and extended droughts in 8% of years

Table 7. Number of recorded droughts, Emerald Airport Seasonal drought Major drought Extended drought (6 months duration) (12 months duration) (24 months duration) No of years 22 21 9 Recorded years 117 117 117 Percentage 19 18 8 Source: Clewett et al. 1999

4.0 GEOLOGY AND LANDFORM

4.1 Geology

The geology of the Emerald 1:250 000 sheet has been described in Veevers et al. (1964) and in Olgers (1969). Galloway (1967) discussed surface geology and geomorphology of the Isaac Comet area, which includes the survey area. The Geological Survey of Queensland has conducted exploration in the area for groundwater (Ishaq 1985) and for coal.

The area consists of: • Quaternary alluvial plains adjoining the Nogoa River (Qa on geology maps); • higher undulating country which consists of late Tertiary to early Quaternary unconsolidated sand and gravel sediments (Cz); and • colluvial cover derived from underlying but non-outcropping early to mid Tertiary sedimentary rocks which are up to 160 m thick (Ta).

The Tertiary sedimentary rocks are composed of claystone with shale, sandstone and conglomerate. Within the survey area, considerable areas of alluvial clay occur in the higher undulating plains. A localised mid Tertiary basalt flow (Tb) is exposed in the bank of the Nogoa River and in creek banks and hillslopes in the west of the survey area. The basalt lies close to the surface north-east of the Nogoa River bridge (Landscape Unit B).

Outcrops were also observed at grid references GR 254,980 and GR 278,010. QWRC drilling logs show basalt occurring intermittently elsewhere in the survey area at depths, which varied from a few metres to 30 m (Lloyd, pers. comm.). These logs, the geological survey logs (Ishaq 1985), and a private well boring log (vicinity GR 244 936), show that unconsolidated clay, sand and gravel are usually found from the surface to 8 m or to below 24 m. Below that depth, alternating sedimentary rocks and clay occur as well as fresh or decomposed basalt. Mudstone was found at 0.2 m to 3.5 m depth and is underlain by basalt at QWRC bore no. 131 (GR 209 967). This mudstone may be part of the Ta geological map unit. Underneath the Tertiary deposits lie Triassic and Permian sedimentary rocks and coal. Pre-Devonian Anakie Metamorphics are found at 1500 m to 2500 m depth.

4.2 Landform

The Quaternary alluvia occur as level plains. The Tertiary alluvia occur as gently undulating rises interspersed with level plains. The basaltic lands form a small, gently undulating plain on the left bank, but only occur in a small area on the western boundary of the study area.

4.3 Landscape units

Landscape units were delineated using geology and landform. Quaternary alluvia were divided into deposits that are more recent, 1A, and older deposits, 6A. The lands on Tertiary alluvia were designated Ts after an early geologic mapping code; it incorporates both Tertiary and some undifferentiated Cainozoic deposits (Cz).

Lands where basalt has influenced soil development were designated as B with the small area of later Tertiary alluvia as 3A. Landscape units 1A, 3A and B relate to landscape units described on the Left Bank (McDonald and Baker 1986); landscape unit 6A is confined to the Right bank survey area (its closest associate in the Left Bank survey area is 2A). A representation of the landscape units is shown in Figure 7.

Landscape Nogoa units 2A B 3A B Tb 2A 1A River 1A 6A Ts

Left Bank Right Bank

Figure 7. Diagrammatic landscape section showing the relative positions of landscape units on the left and right banks of the Nogoa River (McDonald et al. 1984)

Major landscape units Landscape unit 1A (Level plains of recent alluvia) This unit lies adjacent to the Nogoa River. The plain varies in width from less than 100 m (riverbanks) to over 6 km. Depressions and drainage lines are common with levees being absent. Lower lying parts usually have cracking clay soils, while slightly elevated areas have non-cracking clay or duplex soils. Sandier surfaced duplex soils as well as sand are found in the western part of the landscape unit. Flooding is generally in the order of 1 in 14 years (G.Clayton, pers. comm.).

Landscape unit 6A (Level plains on older Quaternary alluvia) This unit is a terrace on higher level plain above landscape unit 1A and is often separated from it by a bank. The plain is usually 2 km to 4 km in width, but narrows to less than 100 m in the centre of the survey area. Drainage lines are much more widely spaced compared to landscape unit 1A and are usually broad and shallow. One creek drains through the landscape unit along the southern limit of map unit 6AUg-3. Soils are predominantly cracking clays. Non-cracking clay soils and thin-surfaced duplex soils occur in areas where former soils are exposed, usually on edges of the plain. Reddish duplex and gradational soils occur on relict levees along parts of the bank at the junction with landscape unit 1A. Some sandier-surfaced duplex soils are found along Winton Creek and in the north-east of the landscape unit. These may be derived from re-deposited sandy alluvia.

Landscape Unit Ts (Gently undulating rises and level plains) This unit is derived from late Tertiary to early Quaternary alluvia and colluvia, which in turn originated from the Tertiary sedimentary rocks. On the gently undulating rises, a catenary sequence occurs: red earths occur on crests; duplex and gradational soils are found on lower slopes; rounded quartz gravel and cobble often underlie the red earth and this may in turn be underlain by yellow or grey clay. Reworking of the alluvia has led to complex soil distribution and some obviously polygenetic soil profiles. Between the rises, gilgaied grey cracking clay soils occur on level plains even though the level plains can be much reduced in parts of this landscape unit, for example in the south-west of the survey area. This landscape unit occupies the bulk of the southern part of the survey area.

Minor landscape units Landscape Unit 3A (Gentle Low Rise) This unit has developed on gravelly and sandy deposits, which are younger than the Tertiary to Quaternary alluvia. The soils are red with gravelly non-cracking clay, gradational and duplex soils. The landscape unit occupies only a very small portion of the survey area; it is much more extensive on the Left Bank (McDonald and Baker 1986).

Landscape Unit B (Gently undulating plain on basalt) The unit has developed on basalt exposed by the removal of over-lying material. Basalt occurs at shallow depths and weathered basalt is usually found within 1.0 m. Dark cracking clays are the main soils found in this unit. The unit is much smaller in area than that found on the Left Bank. Near this landscape unit, landscape units 3A and Ts overlie basalt at depths of 1 m to 5 m.

5.0 HYDROLOGY

5.1 Surface Hydrology

Description The Nogoa River and Winton Creek are not only boundaries of the survey area but the drainage of the area runs into these streams. From the south-east part of the survey area, the watershed between the creeks is marked approximately by Weemah Main Channel. The few minor defined creeks drain the western part of the survey area. The largest of these creeks rises south of the survey area and runs east of Emerald airport north across the Capricorn Highway. It later turns east then north-east along the boundary between landscape units Ts and 6A, continuing through the eastern extension of map unit 6AUg-3 and meandering through landscape unit 1A to the Nogoa river. Drainage apart from these few creeks is via open depressions, which usually do not have banks or streambeds. Many of these depressions as well as the creeks have been converted into defined drains by QWRC during development. These are shown on the soil map.

In landscape unit 1A there are numerous channels, which conduct overflow water from the Nogoa River. The courses of these channels are usually shown by the presence of map units of 1AUg-9 and 1AUg-12. A likely prior bed of the Nogoa River follows map unit 1AUg-10 beginning around the McCosker Weir. Surface drainage of most cracking clay soils is slow because of their low gradients. Cracking clays toward the eastern end of landscape unit 6A, as well as in landscape unit B have better surface drainage because of their slightly higher gradients.

Water Quality Water samples taken at Fairbairn Dam and the start of Weemah Channel between the years 1993 and 1996 show the water to be of good quality, but occasionally turbidity and pH exceed drinking water guidelines (Department of Natural Resources 1998). However, water quality generally deteriorates after leaving Fairbairn Dam because conductivity, pH, turbidity, major ions, nutrients and pesticide level increase due to drainage water from agricultural areas (Department of Natural Resources 1998).

5.2 Sub-surface Hydrology

Description According to farm bores, native-water tables in 1981, prior to irrigation development were at depths of 20 m to 30 m. (D. Nickson, unpublished data). In 1979, the Geological Survey of Queensland drilled six exploration bores in the north-eastern part of the survey area during the Theresa Creek-Upper McKenzie River groundwater investigation (Ishaq 1985). At the time, all these holes were dry. Locations of these bores and their depths are given in Table 8.

In 1982, QWRC established observation bores throughout the Right bank of the EIA. Water has subsequently entered many of these bores. The location of the bores is shown in Figure 8. The location of the QWRC bores as well as depths of each bore, depths to rock or hard layers, shallowest and deepest recorded water levels are all given in Table 9.

Table 8. Location and depths of groundwater investigation bores of the Geological Survey of Queensland on the Right bank, Emerald Irrigation Area, 1979 Bore No. Location* Depth of hole Depth to rock East North (m) (m) 8551-2-32 636100 7407800 100 16 8551-2-33 635500 7407000 100 20 8551-2-34 635100 7405300 102 12 8551-2-35 635300 7404800 36 23 8551-2-36 635200 7404400 182 28 8551-2-37 635200 7403300 36 18 Note: All bores were dry * Australian Map Grid (AGD 1966)

Water in bore 113 lies at shallow depth, and has fluctuated from 1.70 m to 5.50 m below ground level. Water levels in bore 115B fluctuate from 0.35 m to 11.37 m below ground level. Both these bores lie below porous red earth soils and reflect water-tables induced by irrigation and/or seepage from farm water supply ditches or the Weemah Main Channel. Intensive irrigation on red earths and earthy sands south-west of bore 117 will probably result in considerable rise in water-tables in the vicinity of this bore. Water level has fluctuated between 12.2 and 15 m below ground level to date and has a rising trend.

The gleyed duplex soil TsDy-10 that is nearby would have formed under the influences of water perching in the soil following rainfall. The water would have percolated through the red earths and earthy sands upslope. In bore 127, water was recorded at -2.79 m in May 1983. This was probably a response to isolated heavy rainfall. Other bores with water have levels usually in the order of 13 to 16 m, while bores 114A and 131 are deeper. Bores 114A and 115A are rising. Water level in bore 114A has risen from 30 to 10m below ground level.

# 119

# 121

# 120

123 # # 122 130 118 # # 117 # # 125 # 132 # 126 # # 124 131

# 127

#129 113 # # 128 # 116 # 115 # 114

Figure 8. Location of observation bores in the EIA right bank.

Quality According to (D. Nickson, unpublished data), bore waters prior to development were saline with electrical conductivity of 7 to 16 dSm-1. As the bores were mainly in low-lying areas, depths to water were expected to be greater in more elevated areas. This has been borne out by drilling programmes. Water samples collected from QWRC bores in March 1983 (see Table 9) were analysed by the Government Chemical Laboratory (Lloyd and Watts unpublished data). Water in bore 113 had low salt and sodium levels and very low residual alkali. In bore 114, the water had high salt levels, very high sodicity and residual alkali. In bore 123, the water had low salinity, moderate sodicity and high residual alkali. Water in bore 131, had moderate salinity, low sodicity and residual alkali. The data suggested that in general, water tables contained low quality water. The water in bore 113 is an exception, as it will have passed through the porous red earth soil, which is low in salts. Elevated nitrate levels in the sample suggest the leaching of nitrate from irrigation. Sub-surface water is considered unsuitable for irrigation due to the high salinity and high residual sodium carbonate content.

Water-tables Raised water-tables pose one of the greatest threats to longevity and productivity of irrigation areas. Curry et al. (1967) report that it has been shown that 1.2 m is about the critical depth for a saline water-table in the Murray River Irrigation areas. They reported experiments, which showed that once water-tables rise above this depth, no forms of surface drainage or of soil treatments are effective until the water-table is lowered. Once water-tables rise to within 1.2m of the surface, water is drawn to the soil surface by capillary action. Seepages or wet areas develop. If the water is saline, or picks up salt from the soil while moving to the surface, salts will concentrate rapidly on the surface and form salt scalds. Non-saline seepages may even form salt scalds, because what little salt is present in the water may eventually be concentrated sufficiently to form a scald.

A widespread general rise of water-tables under the cracking clay soils poses a great threat. This would be most alarming in cracking clay soils in landscape units 6A and Ts, as those soils have considerable salt lodes. General water-table rises can result if water builds up in the soil from irrigation over a period of time. Currently it seems that water-tables under the cracking clays are at safe levels. However, monitoring of them will remain an essential part of management of this section of the EIA.

Irrigation of porous soils on the undulating rises needs to be very carefully managed. Otherwise, seepages and salinisation, as discussed earlier will degrade the soils adjoining the bases of the rises. This form of salinisation is called landscape salinisation. It may occur in any landscape unit where permeable soils overlie less permeable soils with saline subsoils. In the right bank section of the EIA, most concern would be the red earth and solodic/solodized solonetz catena and similar landscapes in the Ts unit. QWRC monitoring bores will assist in assessing risks. However, water-table rises in landscape situations may be localised. Many impending outbreaks of seepage or salinisation may not be known until symptoms appear on the soil surface.

Table 9. Location, elevation, depth of bore and water levels in QWRC observation bores Bore No Location Aust. Map Elevation (m) natural Depth Depth of bore Shallowest water level below Deepest water level below Remarks Grid surface State datum slots (m) natural surface natural surface (AGD 1966) of drilling to hard rock or Depth (m) Date Depth (m) Date hard bands 113 617700 7393520 182.04 22.0 19.0 4.3 -1.25 1 Mar 1984 -3.40 29 Aug 1990 114A 623600 7392340 188.11 100.0 27.8 26.0-29.0 -11.61 29 Aug 1990 -29.88 24 Jan 1984* Rising 2.8m/yr 114B 623600 7392340 188.11 23.2 15.6-18.6 -10.37 21 Jun 1990 -15.23 12 Oct 1982 Rising 115A 623700 7392650 184.63 33.4 26.9-29.9 -8.65 29 Aug 1990 -29.89 24 Jan 1984* Rising 3.3m/yr

115B 623700 7392650 184.63 33.4 8.4-11.8 -6.78 16 May 1983 -11.37 12 Octl982 116 623800 7393100 183.39 19.6 11.8-15.0 -13.29 21 Jun 1990 -15.40(dry) 25 Oct 1985 Dry 22 Feb 1983 to 25 Oct1985 117A 629060 7399580 172.05 100.0 40.6 14.0-17.0 -13.10 29 Aug 1990 -14.71 4 Oct 1983 Dry 13 Jun 1984 117B 629060 7399580 172.05 100.0 40.6 3.0-6.0 - 6.6 1 (dry) Dry

118 628030 7399840 174.26 15.0 63-8.5 -8.48 16 May 1983 - 8.50(dry) Usually dry

119 633240 7406200 164.69 24.0 21.2 11.2-17.2 -16.07 12 Jun 1984 -17.82(dry) Usually dry 17 120 636608 7403047 162.92 19.6 17.1 12.0-18.0 -15.79 12 Feb 1986 -18.42(dry) 29 Mar 1983 121 634610 7404430 165.84 19.6 11.8 9.2-15.2 -15.32(dry) Dry

122 627770 7400560 171.51 17.6 93-14.8 -14.80(dry) Dry 123 627400 7401040 169.16 24.0 6.6-19.6 -13.81 23 Mar 1984 15.69 11 May 1989 124 624540 7497300 172.29 15.0 8.0-10.0 -10.00(dry) Dry 125 623300 7498860 171.49 10.4 7.4-9.4 -9.4 (dry) Dry

126 623600 7398460 176.55 19.6 14.2-16.2 -16.19(dry) Dry 127 619720 7395320 184.36 10.4 5.4 6.0-9.0 -2.79 16 May 1983 -9.00 (dry) Usually dry 128 619180 7393260 185.80 19.6 11.2-13.2 -13.20(dry) Dry 129 616300 7393760 180.94 22.0 18.7 8.4-10.4 -10.39(dry) Dry

130 621580 7399300 174.53 12.6 11.2 10.6-12.6 -12.70(dry) Dry 131 620900 7396900 183.80 100.0 3.5 13.0-15.0 -9.95 21 Jun 1990 -12.59 23 Feb 1983 132 621430 7398120 177.69 19.6 15.0-18.0 -14.13 21 Oct 1982 -17.71 25 Jul 1989

Notes: Bore no. : full number is preceded by digits 13020 eg 113's full no. is 13020113. Letters A and B indicate 2 bores at the one site. Paired pilot pipes at bores 114, 115 and 117: Pipe A is always the deeper pipe; a cement plug separates the water -tables between the two pipes. Raw data provided by QWRC includes height of reference point (top of casing) above ground level. The data here have been converted to depth below ground level Sand back fill extends over a greater depth than the bore slots. The data include observations from 12 October 1982 to 29 August 1990, except for bore no. 120 where readings ceased on 12 February 1986. * Also dry before this date.

Source: Jeff Lloyd, Natural Resources and Mines, Rockhampton, Queensland.

6.0 NATURAL VEGETATION

About half the survey area had been cleared of natural vegetation when the survey was conducted. Most clearing had been undertaken on the cracking clay soils of landscape units 6A, Ts and B. These areas were under cultivation or pasture. During the 1930’s, much of one property, Codenwarra, had been thinned of other species leaving little-leaved bauhinia, Lysiphyllum carronii, as open woodland.

Vegetation was described using the structural form proposed by Specht (1970), but modified according to Boyland (1974). Here it was attempted to establish the definitive stratum by means of biomass rather than by height. Vegetation for each soil type is summarised in Table 9. The species encountered in the survey area are listed in Appendix 4.

6.1 Vegetation on Landscape Unit 1A

Structural forms Open woodlands to woodlands are the main structural forms. Grasslands or more sparsely timbered open woodlands occur in low lying areas which are regularly inundated. On harder surfaced non-cracking clays and duplex soils (1AUf-7 and 1ADb-7 respectively), shrubby open woodlands occur. Shrublands sometimes occur on the duplex soils.

Species Brigalow (Acacia harpophylla), little-leaved bauhinia (Lysiphyllum carronii) and coolibah (Eucalyptus coolabah) are the main tree species. Coolibah spreads due to major floods. It is much more common in temporary drainage lines and regularly flooded areas. Silver-leaved ironbark (Eucalyptus melanophloia) is common in some areas. An open forest exists on cracking clay, which has bleached horizons, 1AUg-15, in place of coolibah, at GR 303 038. Some of these occurrences may possibly relate to landforms buried by alluvia from the Nogoa River. Boonaree (Alectryon oleifolius) and an occasional poplar box (Eucalyptus populnea) are found. The main shrub on slightly elevated non-cracking clay soils and duplex soils is false sandalwood (Eremophila mitchellii). Yellowwood (Terminalia oblongata) is common on many soil types, possibly with a slight preference for better drained areas. Sally wattle (Acacia salicina), some wilga (Geijera parviflora) and other shrubs also occur.

In the ground layer, currant bush (Carissa ovata) is not widespread, except on slightly elevated soil types such as 1ADb-7, as it is intolerant of flooding. Blue grasses (Dicanthium and other species) are the main grasses, particularly on clay soils. Little grass cover may exist where shrubs or trees are dense. In low-lying areas, sedges (Cyperus species) are components of the ground flora. In depressions where water may pond for some time, bare areas may exist for a considerable period following the eventual drainage and evaporation of water.

6.2 Vegetation on Landscape Unit 3A

The vegetation on this small landscape unit has been highly disturbed. Original vegetation consisted of open woodland with silver-leaved ironbark (Eucalyptus melanophloia), pink bloodwood (Corymbia erythrophloia), and ironwood (Acacia excelsa) being the main tree species.

6.3 Vegetation on Landscape Unit 6A

Structural forms Open woodlands, woodlands or open forests are the principal structural forms. Those often have a dense shrubby understorey. Shrublands are common on duplex soils. More sparsely timbered open woodlands occur in low drainage depressions where water may pond temporarily, for example on mapping unit 6AUg-5. Whipstick brigalow, a clustered low open woodland of brigalow occurred on 6AUg-12 map unit at GR 352 024. Both grassland and open woodland occurred on mapping unit 6AUg-8. Grassland existed on the elevated map unit of 6AUg-4 at GR 240 980, giving rise to it being known locally as 'downs'. Grassland was found occasionally on other clay soils.

Species On clay soils the main tree species were brigalow (Acacia harpophylla), little-leaved bauhinia (Lysiphyllum carronii) and whitewood (Atalaya hemiglauca). Coolibah (Eucalyptus coolabah) occurred regularly on 6AUg-5, a low-lying soil, and on other soils where flooding was more likely to occur. The dominant shrubs on the clay soils were yellowwood (Terminalia oblongata) and false sandalwood (Eremophila mitchellii). Wilga (Geijera parviflora) occurred much less frequently. The ground layer consisted mainly of tussock grasses: bull mitchell grass (Astrebla squarrosa), blue grasses (Dicanthium and other species), feather-top wire grass (Aristida latifolia) and other grasses. Currant bush (Carissa ovata) also occurred. Sedges (Cyperus species) inhabited wetter spots.

Most thin-surfaced duplex soils, principally 6ADb-1, have the same species as those on the cracking clay soils. False sandalwood (Eremophila mitchellii) and currant bush (Carissa ovata) are more abundant while yellowwood (Terminalia oblongata) is much less abundant. As the surface soils of the duplex soils become deeper, poplar box (Eucalyptus populnea) becomes a more important component, while brigalow (Acacia harpophylla) becomes less common or is absent. In the sandier and deeper-surfaced duplex soils, silver-leaved ironbark (Eucalyptus melanophloia) becomes the prominent tree species. As well, the flora becomes much more diverse with many minor tree and shrub species. The non-cracking clay soils have vegetation similar to the thin-surfaced duplex soils. The more porous gradational and duplex soils along the abandoned levee, 6AGn, 6ADb-2, 6ADb-3 have vegetation more characteristic of better drainage such as silver-leaved ironbark (Eucalyptus melanophloia) and large-leaved bauhinia (Lysiphyllum hookeri).

6.4 Vegetation on Landscape Unit Ts

Structural forms Woodland to open woodland is usually the main structural form. On the more deeply gilgaied soils, TsUgg-1 and TsUgg-2, open to closed forests occurred. Woodlands to open woodlands were the principal vegetation forms on the gradational and duplex soils. However, shrubby understoreys or shrublands were more common. Non-cracking clays had formations between those of cracking clays and duplex soils, depending on which soil they more closely resembled. For example, TsUf-3 had vegetation more like thin-surfaced duplex soils such as TsDb.

Species Within this landscape unit, the lighter (sandier) textured soils generally supported a wider range of both tree and shrub species than did the heavier (more clayey) textured soils. The lighter textured soils include the sands, and duplex and gradational soils with deep sandy A or A and B horizons. The heavier-textured soils include cracking and non-cracking clays, duplex soils and some gradational soils with shallow to moderately deep A horizons and clay B horizons. The depth limit of A horizons is probably about 0.5m. The species fall into two groups: • those which grow on both light and heavy textured soils; and • those which are specific to light textured soils.

The heavier textured soils, therefore, support plants of the first group only, while the light textured soils support both plants groups. Species in the first group include brigalow (Acacia harpophylla), little-leaved bauhinia (Lysiphyllum carronii), Dawson gum (Eucalyptus cambageana), whitewood (Atalya hemiglauca), bottle tree (Brachychiton rupestre), poplar box (Eucalyptus populnea), false sandalwood (Eremophila mitchellii), yellowwood (Terminalia oblongata), currant bush (Carissa ovata), nipan (Capparis lassiantha) and supplejack (Ventilago viminalis).

The lighter textured soils support the following species: ironwood (Acacia excelsa), large- leaved bauhinia (Lysiphyllum hookeri), beefwood (Grevillea striata), bootlace oak (Hakea lorea), silver-leaved ironbark (Eucalyptus melanophloia), ghost gum (Corymbia papuana), Moreton Bay ash (Corymbia tessellaris), bitter bark (Alstonia constricta), red ash (Alphitonia excelsa), white bark (Denhamia oleaster), quinine berry (Petalostigma pubescens) and purple bush pea (Hovea longipes).

Comparison of a TsGn-5 and TsUgg-1 soils shows distinct vegetation changes. The yellow earth overlying buried soils (TsGn-5) supports plant communities from tall shrubland to shrubby open forest and 42 species were found on it. The moderately gilgaied grey clay (TsUgg-1) supports a closed or open forest containing only 9 species.

An unusual occurrence was a stand of coolibah in a small elevated swamp at GR 240 934 (Map unit TsUg-8). Coolibah is rare on most of this landscape unit, being mostly confined to the flood prone alluvial landscape units, and lands beside the Nogoa River. Here the coolibah was well above flood height and away from any current streams.

Sally wattle (Acacia salicina) and pink bloodwood (Corymbia erythrophloia), generally being restricted to the light textured soils, are also prominent on the basaltic cracking clays (BUg-2). Sally wattle also occurs on some alluvial clays.

Certain plants show preferences throughout the area for particular soil characters and their greatest densities occur on soils with these characters. Ironwood (Acacia excelsa) occurs mainly on soils with coarse textured A horizons more than 0.3 m thick and with impedance to drainage in the B or D horizons. Wiregrass (Aristida ramosa) grows on soils with at least 0.3 m of well-drained, coarser textured A and B horizons, with or without a subsoil drainage restriction. It grows taller and denser as the depth to any drainage restriction increases. This latter characteristic allowed mapping of the boundaries of the deep red earths, TsGn-3.

Belah (Casuarina cristata) appears to prefer a good water supply as it was found near gilgai, especially the deep gilgai of the TsUgg-1 and TsUgg-2 soils and the perched swamp (TsUg-8). Cypress pine (Callitris glaucophylla) prefers sands or loamy sands to a clayey B or D horizon. Fire in pasture management practice has masked the true status of this plant, which is as susceptible to fire as its timber is resistant to termites. This explains the presence of stands of dead cypress pine in areas where no living plants can be found.

False sandalwood (Eremophila mitchellii), although ubiquitous, shows a preference for an extended water supply such as around gilgai and in soils with seasonal perched water tables. Thus, it is rarely found on deep red earths (TsGn-3). It also appears to be tolerant of saline subsoils. Dawson gum (Eucalyptus cambageana) is generally restricted to soils with very shallow, hardsetting, massive, medium to heavy textured A horizons with low infiltration rates, and which are underlain by bleached A2 horizons over grey-brown clay B horizons. Soil pH is acid to neutral at the surface, with alkaline upper B horizons and neutral to alkaline lower B horizons. Poplar box (Eucalyptus populnea) shows tolerance of saline clay subsoils. It is found most frequently on the yellow to grey duplex soils with thin A horizons and alkaline B horizons. Leopard wood (Flindersia dissosperma) is confined to medium to heavy textured soils with acid subsoils.

Four plants, (Grewia scabrella), purple bush pea (Hovea longipes), hop bush (Dodonaea viscosa subsp. anguatissima) and false sandalwood (Eremophila mitchellii) have revegetated the red and yellow earths with a dense cover after clearing. However, as previously noted, false sandalwood avoids the deep red earths (TsGn-3).

6.5 Vegetation on Landscape Unit B

Almost all this landscape unit had been cultivated. However, tussock grasslands of blue grass (Dicanthium and other species) would have been predominant. Black spear grass (Heteropogon contortus) occurred on map unit BUgg-3. Pink bloodwood (Corymbia erythrophloia), sally wattle (Acacia salicina) and occasionally silver-leaved ironbark (Eucalyptus melanophloia) were trees which dotted the landscape. Brigalow (Acacia harpophylla) was found in some locations on small areas of deeper soils, similar to those occurring on deeply weathered basalts of the left bank area (landscape unit Tb) (McDonald and Baker 1986).

7.0 SOILS

7.1 Soil Distribution

Influence of prior streams The alluvial plain in the south of the survey area that is covered by the large extent of TsUg-7 soil appears to have formed by deposition from a previous course of the Nogoa River. There were probably several previous courses of the river, suggested by the isolated relict pockets of TsGn and TsDy soils north of the Capricorn Highway. There has since been subsequent deposition of younger material further north, shown by the presence of the 6A alluvial plain, and the lower lying 1A alluvia.

In the higher lying areas of the Ts zone some remnants of previous drainage lines can be found; for example the TsUf-6 and TsUg-9 soils are probably associated with an abandoned steam channel, made up of TsUg-9 that is surrounded by the reddish non-cracking clay TsUf- 6. They may have been deposited by a prior stream flowing from an area of clay country over lighter textured soils, such as the nearby TsGn-4 or its predecessors.

The TsUg-8 soil is the main soil of a perched swamp (which has since been drained following irrigation development). The raised main circular depression and other components appear to have been part of a prior stream that was filled up and has been eroded away elsewhere in the landscape (D. Blandford, pers. comm.). Another similar feature appears on aerial photographs to the south and outside the survey area, but has not been investigated.

In the 6A landscape unit, the 6ADr and 6AGn soils have a similar appearance and form part of abandoned levees that have been left relict by prior courses of the Nogoa River, probably flowing at a higher elevation than the current stream. Similar features are also evident in areas of the 1A landscape.

Quaternary deposits In more active alluvial areas, the upper layers of the Tertiary materials have been stripped away. The resulting alluvial deposits are considered as Quaternary with landscape unit 6A being older and landscape unit 1A being younger. Flooding is still active over most of landscape unit 1A and low areas of landscape unit 6A in the east. Frequency of flooding is about one in 14 years (G. Claydon, QWRC, pers. comm.). Much less frequent flooding occurs on the bulk of landscape unit 6A. However in major floods, much of it is inundated. Soil development has been governed principally by the deposition and stripping of soils under alluvial action.

Landscape unit 1A Cracking clays are the most widespread soils. These are usually darker than the cracking clay soils in landscape unit 6A. Thin surfaced duplex soils and related non-cracking clay (1AUf-7) are the next most common soil. Thin to thick surfaced duplex soils are found, particularly in the western part of the landscape unit. Only one soil type is sandy throughout, 1AUc, a minor soil type within 1ADb-9. All other soils have clayey textures; in the case of cracking and non- cracking clays, clayey textures occur from the surface. Almost all profiles show evidence of former soils within the lower profile, but frequently these buried soils are lighter in texture. Dark, brown, or red colours are found in the landscape unit.

No yellow, yellow-brown or yellow-grey colours are found in the surface soils or subsoils. Yellow-brown colours are sometimes found in underlying former soils.

Cycles of deposition and removal of soil have given the landscape unit its appearance and soil characteristics. The current soils pattern, particularly in the eastern part of the survey area seems to have developed in response to alluvial action over a level plain. Cracking clay soils have probably formed in channels and low areas, which were cut into the plain by floodwaters. Thin-surfaced duplex soils occur in inter-channel areas. Variations in some of the cracking clays are probably due to different depths of removal of original overlying soil. For example in the area at GR 307 046, 1AUg-12 has brown clay lower subsoils, while 1AUg- 18 has brown clay throughout. Other variations would be due to differences which occurred when the original deposits were laid down. Cracking clay soils may have formed in the subsoils of the earlier soils following the removal of harder and/or sandier surfaces. Subsequent deposition of darker soils has probably played a part. However, the relative importance of these processes is not known. Deposition has obviously been dominant in 1AUg-10 in which dark clay continues to depths greater than 1.5 m. Similarly, subsequent surficial deposition may also have influenced the development of the dark duplex soil 1ADd- 4.

Landscape unit 6A The principal soils are cracking clays often overlying clays and/or lighter textured soils of different origin. Thin surfaced duplex soils have probably formed by deposition of lighter materials over clays, coupled with some weathering and development of bleached horizons above the clay. Some thicker surfaced duplex soils are also found. The thin surfaced duplex soil 6ADb-1 seems to have formed around the edges of the landscape unit and in other areas where brownish-coloured subsoils became exposed. Reddish duplex soils, deeper browner duplex soils, or those with much fine sand may be remnants of levees or other deposits associated with higher and/or more southerly prior courses of the Nogoa River. Higher levels of total potassium in 6ADr (sample site 27) suggest deposition that is more recent.

The yellow-brown sodic soils and yellow duplex soils in the east of the landscape units may possibly be relict areas, which relate more to older landscape units. This is suggested by the sandy surfaces of some of the duplex soils.

However, total potassium contents of sampled soils are more in keeping with other sites in landscape unit 6A (sample sites 29, 6ADy-3; and 30, 6ADy-6). The eastern map unit of 6AUg-4 (GR 240 980) is in parts hard setting and has a veneer of sand; may have been once a duplex soil with the original A horizon removed by alluvial action and a more friable surface has not yet developed.

Tertiary sediments The Tertiary sediments are believed to have once covered most of the survey area including the basalt. Of significance is the general composition of the uppermost layers. On top were the parent materials from which the red earths and earthy sands were derived. These deposits overlie grey to yellow clay and, at the contact, rounded siliceous gravel and cobbles were found. These deposits still exist and are shown as red earths TsGn-1 to -3 lying above sodic soils such as TsDy-1, which have formed in the exposed grey to yellow clay. The red colour with the relatively sharp contact (to grey and yellow clay, with the presence of rounded gravel and cobbles) suggests that much of the weathering to the coarse textured red earths and earthy sand occurred elsewhere. The red sandy material was subsequently re-deposited over the grey to yellow clay. McDonald and Baker (1986) suggest that the 3A units on the Left Bank area of the Nogoa River formed in this manner. The same process may also have occurred earlier on the Right bank to provide parent materials for the red earths.

Soil formation subsequently was dependent on erosion of the red sandy material and the underlying clay. Remnants of these deposits exist as gentle rises and low rises. Red earths and (red) earthy sands of varying depths are found. Where the red sandy material has been removed, lag gravels and cobbles may be found (soil types TsKa, TsKb, or deposits of gravel on other soils). Complete removal of the red sandy materials has resulted in soils forming on the grey to yellow clay. The principal soils are TsDy-1 and TsDy-4, but reworking of the deposits, weathering and leaching have resulted in a variety of related soils forming on the undulating slopes. At the base of the undulating rises, thin surfaced solodized solonetz and solodic soils have developed, TsDb and TsDy-2 soil types. These have formed by colluvial and alluvial action. This was evident in the horizons seen in the pit dug at GR 192 927 (Site Db, Shaw and Yule 1978). Variability in TsDb map units, particularly near creek lines, can be very high.

The level plains consist of gilgaied grey clays and black earths. These have most likely been formed by alluvial action and are probably old deposits of the Nogoa River. Source of the parent material is unknown but probably had a wide range varying from Tertiary sediments and basalts to the mudstones of the Drummond Range area. McDonald and Williams (1985) suggested that this alluvial clay may once have covered the whole of this landscape unit. An alternative hypothesis is that the cracking clays have formed in older sediments under the grey and yellow clay deposits. Map units TsUf4-Ugg-2, GR220 933; and TsUf4-Ug-7 at GR 209 941 have gravelly or cobbly non-cracking clays on mounds and cracking clay soils in depressions. These may be contact areas where the lag gravels from the later sandier deposits covered parent material for the cracking clays. Bore logs (QWRC unpublished data) mention varieties of grey and brown clay at depth in the landscape unit, but no pedological inferences can be drawn from the general descriptions.

Cracking clay soil types in the Ts landscape units (TsUg) have been distinguished according to depth of gilgai. The bulk of the grey clays are in soil type TsUg-7 whose depth limit for gilgai is <0.3 m. Gilgai in most other TsUg soils also fall within this depth range. Soil types TsUg-2 and TsUg-3 have little gilgai. Soil type TsUgg-1 has gilgai from 0.3 to 0.6 m deep while soil type TsUgg-2 has gilgai >0.6 m deep. Differences between mound and depression profiles can often be detected even when gilgai depths are very shallow (<0.05 m). However, this is not always the case (particularly in younger landscape units where differences seem to become more obvious when vertical intervals exceed 0.25 m).

Tertiary Basalt The soils on the basalt are usually less than 1 m deep. Weathering of the basalt may have been interrupted or at least altered by being covered by the sandier materials and clays during the Tertiary era as discussed above. Following re-exposure, the basalt has weathered to form the moderately shallow cracking clays. Re-exposure into a probably drier climatic regime will have resulted in slower weathering and contributed to the relatively shallow, clayey nature of the soils.

7.2 Mapping Units

The mapping units used in this survey and their dominant and minor soil types are listed in Table 10.

Table 10. Dominant and minor soil types of the mapping units Mapping units Dominant soil type Minor soil types Area (ha) 1AUf-6 1AUf-6 1AUg-9 93 1AUf-6-Ug-9 1AUf-6, 1AUg-9 4 1AUf-6-Ug-13 1AUf-6, 1AUg-13 9 1AUf-7 1AUf-7 1AD6-7 170 1AUf-7-Ug-12 1AUf-7, 1AUg-12 5 1AUf-7-Ug-18 1AUf-7, 1AUg-18 4 1AUg-9 1AUg-9 1AUf6, 1AUg-12 640 1AUg-9E 1AUg-9 4 1AUg-9G 1AUg-9 18 1AUg-9-Uf-6 1AUg-9, 1AUf-6 44 1AUg-9-Uf-7 1AUg-9, 1AUf-7 7 1AUg-10 1AUg-10 1AUg-13 537 1AUg-11 1AUg-11 17 1AUg-12 1AUg-12 1AUf-6, 1AUg-9, 1AUg-13 672 1AUg-12-Uf-7 1AUg12, 1AUf-7 8 1AUg-12G 1AUg-12 11 1AUg-13 1AUg-13 1AUf-7, 1AUg-12, 1AUg-14, 1AUg-18 705 1AUg-15 1AUg-15 1AUg-12 57 1AUg-16 1AUg-16 1AUg-13, 1ADd-4 128 1AUg-17 1AUg-17 1AUf-7 10 1AUg-18 1AUg-18 1AUg-13 101 1AUg-18E 1AUg-18 10 1AUgg 1AUgg 8 1ADr 1ADr 1AUf-7, 1ADb-7 13 1ADb-1 1ADb-1 71 1ADb-3 1ADb-3 7 1ADb-7 1ADb-7 1AUf-7, 1AUg-13, 1AUg-17 298 1ADb-8 1ADb-8 10 1ADb-9 1ADb-9 1AUc, 1ADb-8 112 1ADb-10 1ADb-10 5 1ADd-3 1ADd-3 1AUf-7, 1ADb-7, 1ADd-4 75 1ADd-3-Uf-7 1ADd3, 1AUf-7 1AUf-6, 1AUg-16, 1ADb-7 45 1ADd-4 1ADd-4 454 1ADd-6 1ADd-6 26 Total area of 1A mapping units 4378 cont.

Table 10. continued Mapping units Dominant soil type Minor soil types Area (ha) 3AUf 3AUf 6 3AGn-2 3AGn-2 2 3AGn-Dr 3AGn, 3ADr 2 Total area of 3A mapping units 10 6AUf-1 6AUf-1 6 6AUf-I-Ug-1 6AUf-1, 6AUg-1 6 6AUf-2 6AUg-2 5 6AUf-2-Ug-6 6AUf-2, 6AUg-6 4 6AUf-2-Ugg 6AUf-2, 6AUgg 5 6AUf-3 6AUf-3 6ADb-1, 6AUg-6, 6AUg-10 71 6AUf-3-Ug-6 6AUf-3, 6AUg-6 12 6AUf-3-Ug-10 6AUf-3, 6AUg-10 7 6AUf-4 6AUf-4 6ADb-1 5 6AUf-4-Ug-1 6AUf-4, 6AUg-1 2 6AUf-4-Ug-10 6AUf-4, 6AUg-10 18 6AUg-1 6AUg-1 17 6AUg-3 6AUg-3 6AUg-6, 6AUg-10 371 6AUg-3-Uf-2 6AUg-3, 6AUf-2 20 6AUg-4 6AUg-4 6AUg-3, 6AUg-10 127 6AUg-5 6AUg-5 6AUg-6, 6AUg-8, 6AUg-10 182 6AUg-6 6AUg-6 6AUg-8, 6AUg- 10 486 6AUg-6-Uf-2 6AUg-6, 6AUf-2 24 6AUg-7 6AUg-7 64 6AUg-8 6AUg-8 6AUg-6, 6AUg- 10 117 6AUg-8-Uf-3 6AUg-8, 6AUf-3 5 6AUg-9 6AUg-9 6AUg-6, 6AUg-10 122 6AUg-10 6AUg-10 6AUg-6, 6AUg-8, 6AUg-12 1196 6AUg-10-Uf-3 6AUg-10, 6AUf-3 186 6AUg-10-Uf-4 6AUg-10, 6AUf-4 6AUg- 11 37 6AUg-10-Ug-6 6AUg-10, 6AUg-6 124 6AUg-10-Db-1 6AUg-10, 6ADb-1 2 6AUg-12 6AUg-12 6AUg-6, 6AUg-8, 6AUg-10 561 6AUgg 6AUgg 2 6AGn 6AGn 3 6ADr 6ADr 6AGn, 6ADbA, 6ADb-3 146 6ADb-1 6ADb-1 6AUf-3, 6AUf-4, 6AUg- 10, 6AUg- 11, 368 6ADd-1, 6ADd-2 6ADb-1E 6ADb-1 28 6ADb-2 6ADb-2 7 6ADb-3 6ADb-3 18 6ADb-4 6ADb-4 6 6ADb-4-Ug-5 6ADb-4, 6AUg-5 13 6ADb-5 6ADb-5 2 6ADy-1 6ADy-1 6AUg-12 17 6ADy-2 6ADy-2 6AUg-5 26 6ADy-3 6ADy-3 6ADy-1 36 6ADy-4 6ADy-4 4 6ADy-5 6ADy-5 7 6ADy-6 6ADy-6 30 6ADd-1 6ADd-1 6ADbA, 6AUg-3 37 6ADd-2 6ADd-2 3 Total area of 6A mapping units 4535

cont.

Table 10. continued Mapping units Dominant soil type Minor soil types Area (ha) TsUc-1 TsUc-1 TsKb 9 TsUc-2 TsUc-2 TsGn-3, TsDy-1, TsDy-5, TsDy-7 126 TsUc-3 TsUc-3 9 TsUf-1 TsUf-1 TsUf-3, TsUg-1, TsDb, TsDy-2 115 TsUf-1-Ug-4 TsUf-1, TsUg-4 20 TsUf-1-Db TsUf-1, TsDb 2 TsUf-2 TsUf-2 TsUf-3, TsUg-7, TsDb 23 TsUf-2-Ug-7 TsUf-2, TsUg-7 TsUg-1, TsUg-7, TsDb 12 TsUf-3 TsUf-3 TsUg-1, TsUg-7, TsDb 91 TsUf-3-Uf-2 TsUf-3, TsUf-2 30 TsUf-3-Ug-7 TsUf-3, TsUg-7 18 TsUf-4 TsUf-4 49 TsUf-4E TsUf-4 2 TsUf-4-Ug-7 TsUf-4, TsUg-7 26 TsUf-4-Ugg-2 TsUf-4, TsUgg-2 3 TsUf-6 TsUf-6 TsUg-9, TsGn-6, TsDr-1 31 TsUf-6-Ug-9 TsUf-6, TsUg-9 50 TsUf-7 TsUf-7 9 TsUg-1 TsUg-1 25 TsUg-l-Uf-1 TsUg-1, TsUf-1 25 TsUg-l-Uf-4 TsUg-1, TsUf-4 4 TsUg-2 TsUg-2 20 TsUg-3 TsUg-3 TsUf-4, TsDb 11 TsUg-7 TsUg-7 TsUf-1, TsUf-2, TsUf-3, TsUg-1, TsUgg-1, 1830 TsDb TsUg-7-Dy-9 TsUg-7, TsDy-9 13 TsUg-8 TsUg-8 TsUf-7 3 TsUg-9 TsUg-9 TsUf-6 7 TsUgg-1 TsUgg-1 TsUg-7, TsUgg-2 78 TsUgg-2 TsUgg-2 TsUg-7, TsUgg-1 112 TsGn-1 TsGn-1 TsKa, TsKb 30 TsGn-2 TsGn-2 TsGn-3, TsDy-7 152 TsGn-3 TsGn-3 TsUc-2, TsGn-4, TsDy-7 199 TsGn-4 TsGn-4 TsUf-6, TsUg-9, TsGn-3, TsGn-6 73 TsGn-4-Gn-5 TsGn-4, TsGn-5 4 TsGn-5 TsGn-5 TsGn-6, TsDb, TsDy-1, TsDy-2, TsDy-6, 229 TsKb TsGn-6 TsGn-6 TsGn-4, TsGn-5, TsGn-10, TsDy-1, TsDy-4, 124 TsKb TsGn-8 TsGn-8 TsDy-1, TsDy-4 18 TsGn-9 TsGn-9 TsUc-3, TsDy-1 31 TsGn-10 TsGn-10 2 TsGn-11 TsGn-11 10 TsGn-12 TsGn-12 2 TsDr-1 TsDr-1 TsUf-6, TsGn-6, TsUg-9, TsDy-1 120 TsDr-1-Dy-1 TsDr-1, TsDy-1 21 TsDr-2 TsDr-2 26 TsDr-3 TsDr-3 2 TsDb TsDb TsUf-1, TsUf-2, TsUf-3, TsUg-1, TsUg-7, 667 TsDy-2- TsDbG TsDb 74 TsDb-Uf-1 TsDb, TsUf-1 9 TsDy-1 TsDy-1 809 cont.

Table 10. continued Mapping units Dominant soil type Minor soil types Area (ha) TsDy-1E TsDy-1 1 TsDy-l-Ug-9 TsDy-1, TsUg-9 TsUf-6, TsDr-1 7 TsDy-1-Gn-9 TsDy-1, TsGn-9 TsUg-1, TsUg-7 73 TsDy-1-Dy-4 TsDy-1, TsDy-4 40 TsDy-2 TsDy-2 TsUf-3, TsUg-7, TsDb, TsDy-1, TsDy-9 57 TsDy-2-Uf-1 TsDy-2, TsUf-1 3 TsDy-2-Ug-7 TsDy-2, TsUg-7 1 TsDy-3 TsDy-3 4 TsDy-4 TsDy-4 TsDy-1 122 TsDy-4-Dy-1 TsDy-4, TsDy-1 8 TsDy-5 TsDy-5 TsDy-1 16 TsDy-6 TsDy-6 TsGn-4, TsGn-5, TsDy-1 45 TsDy-7 TsDy-7 TsUc-2, TsUc-3, TsDy-1, TsDy-4 121 TsDy-8 TsDy-8 TsGn-3, TsGn-5, TsDy-1 83 TsDy-9 TsDy-9 3 TsDy-10 TsDy-10 7 TsKa TsKa TsUf-4, TsGn-1, TsDy-1 79 TsKb TaKb TsUc-1, TsGn-1, TsGn-6, TsDy-1 14 Total area of Ts mapping units 6039 Bug-2 Bug-2 152 BUgg-3 Bugg-3 6 Total area of B mapping units= 158 R Rock 23 Q Quarries 9 Total area of miscellaneous mapping units 32 Total area of survey 15152

7.2 Morphology and classification

A detailed description of each dominant soil type in each mapping unit and associated soil types is given in Appendix 1. The soil types have been classified according to the Australian Soil Classification (Isbell, 1996). The classification of the soils to Subgroup level is shown in Appendix 1.

7.3 Chemical and physical attributes

Following the field survey, representative soil profiles from 36 soil types were sampled for laboratory analysis. The morphological descriptions and laboratory data for these profiles are presented in Appendix 3. The profiles were sampled in 0.1 m increments to 1.5 m, where possible. Bulk surface (0-0.1 m) samples (a composite of 9 sub samples) were also collected for surface fertility assessment. Analyses were performed on samples taken from standard (0.3 m) depths in the representative profiles and also on the bulk surface samples (Table 11). In addition, pH, electrical conductivity and chloride were determined on the samples from intermediate 0.1 m increments. Specific analytical methods and some data interpretations are listed in Bruce and Rayment (1982) and Baker and Eldershaw (1993).

Table 11. Laboratory analyses conducted on soils Soil analysis* Sample type and depth (m) Bulk Profile 0-0.1 0-0.1 0.2-0.3 0.5-0.6 0.8-0.9 1.1-1.2 1.4–1.5 pH, EC, Chloride X X X X X X X Exch. Cations, CEC X X X X X X Total P, K, S X X X X X X Particle size analysis X X X X X X Dispersion ratio X X X X X X Soil moisture @ 1500 kPa X X X X X X Organic C, Total N X Acid extractable P X Bicarb. extractable P X Replaceable K X DTPA extr. Fe, Mn, Cu, Zn X * Baker and Eldershaw (1993)

In addition to the sampled representative soil profiles, soil characterisation data from a further 8 sites were included from relevant sites studied by Shaw and Yule (1978). The chemical data from these sites have not been included here but can be found in Shaw and Yule (1978). Emphasis was placed on the major soil types that occur throughout the study area and hence these soils have the greatest number of profiles analysed. For discussion of chemical characteristics the soil types have been placed into four groups based on differences in landscape and soil formation. These groups are: • Cracking clays (1AUg, 6AUg, TsUg and BUg), • Alluvial duplex soils (1AD, 6AD), • Tertiary sediment duplex soils (TsD), and • Miscellaneous (6AUf, TsUf, TsGn and TsUc).

Each group has been further divided. The cracking clays have been divided on the basis of parent material. The two duplex soil groups have been divided into three categories based on A horizon thickness, namely • less than 0.1 m (thin); • 0.1 to 0.3 m (moderately thick); and • 0.3 to 0.6m. (thick).

The miscellaneous group mainly includes minor soils. The groups, subgroups and number of profiles analysed are shown in Table 12.

Table 12. Groups, subgroups and number of profiles analysed Number of soil Soil group Subgroup Description of subgroup profiles analysed Cracking clays 1AUg Lower alluvia parent material 3, 1* 6AUg Higher alluvia parent material 8,1* TsUg Tertiary sediments parent material 10,2* BUg Basaltic parent material 1* Alluvial duplex soils 1AD Lower alluvia parent material 3 6AD1 Higher alluvia, thin A horizon 4 6AD2 Higher alluvia, moderately thick A horizon 1 6AD3 Higher alluvia, thick A horizon 1 Tertiary sediment TsD1 Tertiary sediments, thin A horizon 2, 3* duplex soils Tertiary sediments, moderately thick A TsD2 3 horizon TsD3 Tertiary sediments, thick A horizon 1, 1* Miscellaneous soils 6AUf Higher alluvia, non cracking clays 2 TsUf Tertiary sediments, non cracking clays 3 TsGn Tertiary sediments, gradational soils 10 TsUc Tertiary sediments, uniform sands 1 * From Shaw and Yule (1978)

Soil pH The mean soil profile pH (1:5 soil/water) for each soil group has been plotted and is shown in Figures 9 to 12. pH pH 45678910 45678910 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5

1AUg 6AUg TsUg BUg 1AD 6AD1 6AD2 6AD3

Figure 9. Mean pH for the cracking clays Figure 10. Mean pH for the alluvial duplex soils

pH pH 45678910 45678910 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5

TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc

Figure 11. Mean pH for the Tertiary Figure 12. Mean pH for the miscellaneous sediment duplex soils soils A more detailed account about soil pH of the cracking clays in the study area can be found in Tucker (1984), where an attempt was made to correlate pH with: • soil depth; • landscape unit ; and • two example soil types (6AUg-10 and TsUg-7).

There is high variation in soil pH of the cracking clays across all landscapes. Therefore care needs to taken when interpreting the average pH values used in this discussion. According to Tucker (1984), some of the variation was caused by small sample sizes used in the analysis. The same warning applies to the alluvial and Tertiary sediment duplex soils and the majority of the miscellaneous soils group in the following discussion.

The cracking clays in the lower alluvia (1A) are moderately to strongly alkaline throughout the profile with a slight bulge between 0.3-0.8 m (Figure 9). The cracking clays of the higher alluvia (6A) are moderately to strongly alkaline to approximately 1 m with a pH decrease to neutral at depth. The cracking clays overlying Tertiary sediments are neutral to slightly alkaline at the surface becoming alkaline in the subsoil, and then pH decreases rapidly to moderately acid in the lower subsoil. The cracking clays of the Basalt landscape (B) show a gradual increase in pH from 7.0 on the surface to 8.0 at depth.

Depth to increased pH in the alluvial duplex soil group is associated with depth of the A horizon (Figure 10). The moderately thick A horizon soils show the alkaline trend deeper into the soil (at 0.3 m) where the B horizon is found. The thick surface (0.7 m) profile of the 6A landscape has a neutral surface horizon becoming moderately acidic at 0.8 m before the pH increases to a level comparable to the other profiles at 1.5 m.

Tertiary sediment duplex soils (Figure 11) are slightly alkaline in the A horizon, with a rapid increase in pH in the upper subsoil. The soils with thick A horizons are strongly alkaline in the subsoil. Soils with a thin A horizon are also strongly alkaline in the upper subsoil but pH decreases rapidly to neutral at depth. These trends probably reflect the relative leaching of basic ions within the A horizon causing slightly acidic conditions in the surface horizon. This is due to imperfect drainage of the duplex soils, where waterlogging occurs at the boundary of A and B horizons. The presence of a bleached A2 horizon generally indicates that periodic saturation conditions exist. Soils with thicker surface horizons may have a longer history of leaching and hence the more pronounced acidic trend. The Tertiary sediment duplex soils with a thin A horizon have a neutral pH at depth compared to the other soils in the group.

The Ts non-cracking soils of the miscellaneous group (Figure 12) have a strongly alkaline trend in the subsoil. The pH decreases rapidly in the deep acid clay parent material, which typically underlies brigalow (Acacia harpophylla) lands. The Ts non-cracking clays follow the same trend as the Ts cracking clays. The other two soil groups, the uniform sands and gradational soils, tend to be neutral pH throughout, reflecting well drained conditions. Surface soil pH in all soils is unlikely to cause major nutrient availability or toxicity problems, particularly in the top 0.1 m, for most cropping uses.

Soil types with subsoil pH 5.5 or less are shown in Table 13. According to Baker and Eldershaw (1993), growing conditions for all but acid tolerant plants becomes more difficult at pH 5.5 and less. Problems associated with acid subsoils in reducing rooting depth are confined to one soil sub-group, the cracking clays on Tertiary sediments (particularly TsUg- 7); these soils have acid subsoils at depth. For the TsUg-7 soil low pH occurs at 0.6 to 1.1 m depth.

Table 13. Analysed soil types with subsoil pH 5.5 or less Soil Type Depth (m) to pH 5.5 or less* 6AUg-12 1.4 TsDb 1.4 TsUf-3 1.1 TsUg-7 0.6-1.1 TsUgg-2 1.5 * Baker and Eldershaw (1993), pH limit for most plant growth

Salinity Salinity levels were assessed by electrical conductivity (EC) and the chloride content of a 1:5 soil:water suspension for all soils analysed. EC accounts for all salts in the soil, including contributions from less soluble sources of salts such as gypsum. Chloride levels relate to the more common salts such as sodium chloride. Detailed discussions on salinity are contained within Shaw et al. (1987) and Department of Natural Resources (1997). The EC data from Shaw and Yule (1978) profiles used in this study were originally derived from 1:1 extracts. These were subsequently converted to 1:5 equivalents for comparison with the standard analyses. The mean soil profile ECs of the soil groups are shown in Figures 13 to 16. Mean chloride levels based of the soil groups are shown in Figures 17 to 20.

EC (dS/m) EC (dS/cm) 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m) Depth

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg BUg 1AD 6AD1 6AD2 6AD3 Figure 13. Mean EC for the cracking clays Figure 14. Mean EC for the alluvial duplex soils

EC (dS/cm) EC (dS/cm) 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5

TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 15. Mean EC for the Tertiary Figure 16. Mean EC for the miscellaneous sediment duplex soils soils

Chloride (mg kg-1) Chloride (mg kg-1) 0 500 1000 1500 2000 0 500 1000 1500 2000 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5

1AUg 6AUg TsUg BUg 1AD 6AD1 6AD2 6AD3 Figure 17. Mean chloride levels for the Figure 18. Mean chloride levels for the cracking clays alluvial duplex soils

Chloride (mg kg-1) Chloride (mg kg-1) 0 500 1000 1500 2000 0 500 1000 1500 2000 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5

TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 19. Mean chloride levels for the Figure 20. Mean chloride levels for the Tertiary sediment duplex soils miscellaneous soils The trends for chloride down the profile are similar to the EC trends for each soil subgroup, which indicates that sodium chloride is the dominant salt. The majority of the soil groups show a clear relationship between increasing EC and increasing levels of chloride, confirming that the dominant salt in most profiles is sodium chloride. However, the Tertiary sediment duplex soils with a thin A horizon have higher EC than expected for the chloride levels due to the presence of gypsum (calcium sulfate). High total sulphur levels were observed in the TsDb soil type confirming the presence of sulphates.

For the cracking clay group there is a similar EC trend for soils derived from alluvial material (1A, 6A) and Tertiary sediments (Figure 13). The basalt sub-group has low salinity throughout. The cracking clays tend to have increasing EC to 0.9 m depth (maximum 1.05 dSm-1) with a slight decrease with increasing depth. Although these EC readings are moderate to high at depth, it is unlikely that agriculture would be affected in the short term. However, any upward movement of ground water resulting from irrigation may result in saline outbreaks. This has occurred in cracking clays on basalt lying below the Tb landscape units on the left bank of the EIA (Dowling et al. 1984, McDonald and Baker 1986).

The EC values for alluvial duplex soils show a similar relationship, but the 6A soils are moderately saline at depth (Figure 14). The Tertiary sediment duplex soils reflect a salinity trend that relates to the depth to the B horizon (Figure 15). On average, soils with a thick A horizon have low salinity throughout the profile. Salinity increases within the subsoils that have a thin or moderately thick A horizon. However, salinity levels do not exceed moderate levels. The miscellaneous soil group shows two distinct trends: the gradational and uniform sands have very low salinity; and the non-cracking clay soils have similar salinity levels to the alluvial duplex soils (Figure 16).

The drainage of the soil types influences profile salinity. The well-drained soils (TsGn, TsUc) have very low salinity down the profile. The duplex soils range from moderately well drained to imperfectly drained. In particular, a thicker A horizon may allow increased drainage of the soil profile as a whole. The profiles have low salinity in the better drained A horizon, then salinity levels increase in the subsoil where drainage is restricted. Duplex soils tend to have moderate salinity levels in the subsoils, however the soils with a thick A horizon have low salinity in the subsoil. The 6A soils with a thin A horizon have high salinity levels at depth.

The cracking clays (1AUg, 6AUg and TsUg) have similar drainage but show higher EC levels than the duplex soils at shallower depth. A possible reason may be that the cracking clays are younger and hence have less salt removal through drainage. The B unit soils are moderately well drained and are slowly permeable when wet. However, these soils have very low salinity as they are derived from the underlying basalt (McDonald and Baker 1986).

Salinity assessment To accurately assess the impact of salinity on the soils after irrigation, the methods outlined in Shaw et al. (1987) and Department of Natural Resources (1997) were used. The individual 1:5 EC values have been recalculated as electrical conductivity of the saturation extract (ECse). The ECse of the soil is more relevant to soil conditions affecting plant growth under irrigation, because the influence of soil texture on the soil solution is removed.

Plants are more sensitive to salinity at water contents equal to or drier than field capacity. ECse is the most dilute soil solution concentration that plants could be expected to encounter and has been successfully used to relate plant response to soil salinity across a wide range of soil conditions (Shaw et al. 1987). Plant rooting depth is related to the concentration of salts down the profile. According to Shockley (1955), quoted by Shaw et al. (1987), 40% of the soil water uptake by plants occurs in the top quarter of the rooting depth, reducing to 30% in the second quarter, 20% in the third quarter, and 10% in the final quarter. Plant water uptake is estimated by the use of a weighting factor at each increment over the rooting depth of a particular crop.

By use of a regression equation, salt measurements taken at 0.1 m increments can be related to depth fractions of the rooting depth (Shaw et al. 1987), allowing calculation of the weighted root zone salinity for each 0.1 m increment. These results are averaged to the relevant plant rooting depth and compared to the plant tolerances given by Shaw et al. (1987). The final ECse of analysed soil for particular rooting depths are shown in Table 14.

Table 14. Weighted root zone salinity of the analysed soils

-1 1 Soil type Weighted root zone salinity (ECse dSm ) at selected depth ranges 0 - 0.1m 0 - 0.3m 0 - 0.5m 0 - 1.0m 1ADb-7 0.64 1.51 2.50 4.22 1ADd-3 0.41 0.39 0.38 0.86 1ADd-4 1.96 1.30 1.40 2.58 1AUg-9 1.28 0.48 0.37 3.22 1AUg-12 0.55 0.61 0.84 1.52 1AUg-13 0.71 0.84 1.14 4.09 1AUg-16 1.10 1.63 2.29 2.93 6ADb-1* 1.07 2.35 3.88 5.46 6ADb-2 1.43 3.17 4.26 4.77 6ADr 0.20 0.24 0.50 1.35 6ADy-3 0.18 0.28 0.41 1.04 6ADy-6 0.40 0.39 0.36 0.35 6AUf-3 1.01 2.78 3.77 4.26 6AUf-4 2.19 1.85 2.62 3.90 6AUg-4 1.00 1.38 1.80 2.40 6AUg-5 0.39 0.39 0.48 0.98 6AUg-6* 0.87 0.97 1.43 2.50 6AUg-7 1.33 0.65 0.65 7.12 6AUg-8 2.13 3.70 4.65 5.26 6AUg-10* 1.01 1.72 2.66 4.27 6AUg-12 0.52 0.76 1.38 3.17 BUg-2 0.32 0.12 0.08 0.63 TsDb* 0.41 0.50 1.15 2.84 TsDr-1 0.43 0.37 0.37 0.72 TsDy-1 0.65 0.46 0.47 0.71 TsDy-8 0.18 0.18 0.24 0.24 TsGn-2* 0.26 0.31 0.33 0.40 TsGn-3 0.53 0.50 0.46 0.40 TsGn-4 0.30 0.28 0.28 0.27 TsGn-5 0.53 0.41 0.38 0.36 TsGn-6 0.57 0.44 0.38 0.32 TsGn-8 0.32 0.23 0.20 0.23 TsGn-9 0.37 0.27 0.24 0.25 TsUc-2 0.54 0.42 0.48 0.34 TsUf-1 0.94 2.12 3.16 4.11 TsUf-3 0.24 0.77 1.87 3.71 TsUf-6 1.70 2.41 3.25 4.10 TsUg-7 1.21 1.80 2.56 3.71 TsUgg-2** 0.98 1.87 2.89 4.56 Values presented in this table have been based on the crop tolerances given by Shaw et al. (1987).

Green values represent levels for sensitive crops Blue values represent levels for moderately sensitive crops Red values represent levels for moderately tolerant crops Maroon values represent levels for tolerant crops 1 Depths correspond to minimum rooting depths suggested by Irvine (in prep). * Mean values only ** Variable value due to mound and depression samples (Standard Derivation >0.5)

A number of soils have the potential to restrict growth for salt sensitive plants under irrigation which having rooting depths between 0.3 m and 0.5 m. These soils include: 6ADb-1, 6ADb- 2, 6AUf-3, 6AUg-8, TsUf-1 and TsUf-6. At rooting depths of 0.5 m the number of soils with potential salinity (for salt sensitive crops) increases to also include: 1ADb-7, 6AUg-16, 6AUf- 4, 6AUg-10, TsUg-7 and TsUgg-2. A minor number of soils reflect the natural salinity variation that occurs within the subsoils. The TsUgg-2 is an example where four sites were sampled yet had different results due to mound and depression samples.

At rooting depths of 1 m clear trends are found, with the cracking clays (Ug) and uniform non-cracking soils (Uf) across all landscape units having levels suitable for moderately tolerate plants. There are two soils (1AUg-12 and 6AUg-5) that have lower levels. The basalt cracking clay (BUg-2) has no effect on plant growth due to salinity. The alluvial duplex soils (1AD, 6AD) also display a similar trend to the cracking clays. However, the better-drained duplex soils (1ADd-3, 6ADr, 6ADy-3 and 6ADy-6) show a lower level of salinity. The Ts units are similar, where the better drained TsDr-1, TsDy-1, TsDy-8, TsUc-2 and all TsGn units have little salinity throughout. However, the TsUg and TsUf at depth are suited to only moderately tolerant crops. The 6AUg-8 is suited only to salt-tolerant crops with rooting depths of 0.5m. The 6ADb-1, 6ADb-2, 6AUg-7, 6AUg-8 and TsUgg-2 have similar levels at depths of 1 m. A list showing the soils that may have potential salinity problems under irrigation is shown in Table 15.

Table 15. Depth to weighted root zone salinity thresholds of the analysed soils Soil type Depth to weighted root zone salinity threshold (m) moderately tolerant crops1 tolerant crops1 1ADb-7 0.5 1ADd-4 0.1 1AUg-9 1.0 1AUg-13 1.0 1AUg-16 1.0

6ADb-1* 0.3 1.0 6ADb-2 0.3 1.0 6AUf-3 0.3 6AUf-4 0.1 6AUg-4 1.0 6AUg-6* 1.0 6AUg-7 No depth restriction 1.0 6AUg-8 0.1 0.5 6AUg-10* 0.5 6AUg-12 1.0

TsDb* 1.0 TsUf-1 0.3 TsUf-3 1.0 TsUf-6 0.3 TsUf-7 0.5 TsUgg-2* 0.5 1.0 1 -1 -1 Based on the threshold for moderately tolerant crops (ECse dSm >1.91) and tolerant crops (ECse dSm > 4.51) as given by Shaw et al. (1987). * Mean values used

Sodicity Sodicity is measured by the concentration of sodium ions in relation to the soil’s cation exchange capacity. The exchangeable sodium percentage (ESP) is calculated by the following equation: Exchangeable Sodium(Na + ) ESP = ×100 Cation Exchange Capacity (CEC)

For acid soils, the effective cation exchange capacity is substituted in the above formula.

A high level of sodicity causes clays to become more dispersible which restricts water entry and reduces the ability of the soil to conduct water by blocking pores. Sodic soils can become dense, cloddy and structureless on drying because the natural aggregation is destroyed (Department of Natural Resources 1997). Northcote and Skene (1972) devised criteria for the three categories of sodicity in Australian soils: • ESP <6 % - non sodic; • ESP 6-14 % - sodic; and • ESP >15 % - strongly sodic.

In soils with very low CEC and exchangeable sodium values, Isbell (1996) advised caution in the calculation of ESP. Very low values (CEC <3 meq.100g-1 and Na+ <0.3 meq.100g-1) have been excluded from the analysed data in the sodicity calculations. Soils with calcium:magnesium ratios above 2 also tend to reduce the effects of sodicity (see calcium:magnesium ratio). Mean ESP for the soil groups is shown in Figures 21 to 24. The depth to a sodic layer for all analysed soils is provided in Table 16.

ESP (%) ESP (%) 0 3 6 9 12 15 18 21 24 27 30 0 3 6 9 12 15 18 21 24 27 30 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg BUg 1AD 6AD1 6AD2 6AD3 Figure 21. Mean ESP for the cracking clays Figure 22. Mean ESP for the alluvial duplex soils

ESP (%) ESP (%) 036912151821242730 0 3 6 9 12 15 18 21 24 27 30 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 23. Mean ESP for the Tertiary Figure 24. Mean ESP for the miscellaneous sediment duplex soils soils

The ESP values indicate that the BUg, TsGn, TsUc and the alluvial duplex soils with thick A horizon are generally non-sodic. At depth (>0.9 m), some TsGn soils become sodic. The non-cracking clays (6AUf, TsUf) are strongly sodic by 0.4 m. The soils of the higher alluvia have higher ESP levels compared to the lower alluvia soils. The duplex soils have variable subsoil sodicity irrespective of A horizon thickness.

The significant relationship between ESP and EC1:5 is shown in Figure 25. High salinity counteracts the effects of dispersion and in cases of low salinity soils, dispersion can occur at low ESP levels. Sodicity can be a potential problem if salts are leached under irrigation.

3.0

2.5 )

-1 2.0

dSm 1.5 1:5 1.0 0.1657x

(EC y = 0.0817e 2 0.5 R = 0.7506, P < 0.05 Electical Conductivity

0.0 0 3 6 9 12151821242730 Exchangeable Sodium Percentage

Figure 25. Relationship between ESP and EC1:5

Table 16. Depth to sodic and strongly sodic layers in the soils analysed. Depth to sodic1 layer Depth to strongly sodic2 layer Soil type (m) (m) 6ADb-1* 0.1 0.6 6AUg-10 0.1 0.3 6AUg-8 0.1 0.6 TsUf-1 0.1 0.6 TsUf-3 0.1 0.3 1ADb-7 0.3 1.2 1AUg-12 0.3 1.2 1AUg-13 0.3 0.9 1AUg-16 0.3 0.9 6ADb-2 0.3 0.6 6AUf-3 0.3 0.4 6AUf-4 0.3 0.4 6AUg-4 0.3 6AUg-6* 0.3 0.6 6AUg-7 0.3 0.6 TsDb* 0.3 0.6 TsDy-1 0.3 0.6 TsUf-6 0.3 0.6 TsUg-7 0.3 0.6 TsUgg-2 (depression) 0.3 0.6 1ADd-4 0.6 1AUg-9 0.6 6Adr 0.6 0.9 6ADy-3 0.6 0.9 6AUg-12 0.6 6AUg-5 0.6 1.5 TsUf-6 Ug-9 0.6 1ADd-3 0.9 TsGn-2* 0.9 TsGn-5 0.9 TsDr-1 1.2 TsGn-8 1.2 6ADy-6 Non-sodic BUg-2 Non-sodic TsDy-8 Non-sodic TsGn-3 Non-sodic TsGn-4 Non-sodic TsGn-6 Non-sodic TsGn-9 Non-sodic TsUc-2 Non-sodic 1 Exchangeable Sodium Percentage 6 – 15% 2 Exchangeable Sodium Percentage > 15% * Mean

Cation exchange capacity Cation exchange capacity (CEC) is a measure of the total capacity of a soil to hold exchangeable cations (Rengasamy and Churchman 1999). Consequently, the CEC is used as an indication of the potential storage and availability of nutrients for plant growth. The CEC was determined using an extracting solution at pH 8.5. This procedure approximates field values if soil pH is at a similar level. The majority of the soils analysed had an alkaline trend, however, some soils were neutral to acid at depth and this procedure will have underestimated CEC. The significant relationship between CEC and clay content is shown in Figure 26.

Clay % = 5.0839 (CEC) 0.6638 Clay Percentage 20 R2 = 0.8179, P < 0.05

0 020406080 CEC (m.equiv.100g-1) Figure 26. Relationship between CEC and clay percentage

The mean CEC for the soil groups is shown in Figures 27 to 30. In the duplex soils, CEC increases within the B horizon due to an increase in clay content. The cracking clays on basalt have the highest CEC of all soils (76 meq. 100g-1 at 0.6 m). However, the CEC within this soil decreases within the weathering basalt. The other cracking clay soils have uniform but lower CEC. Within the miscellaneous soil group the gradational soils and uniform sands are similar but have lower CEC than the cracking clays due to their lower clay contents. The non- cracking clays have a low CEC at the surface because of lower clay content, increasing to a level in the subsoil similar to the alluvial cracking clays and alluvial duplex soils.

Calcium:magnesium ratio Exchangeable magnesium, in association with sodium, has been shown to aid soil dispersion in some soils (Emerson and Bakker 1973). Shields and Williams (1991) discussed occurrences of poorly structured clay subsoils with low ESP, but with significant magnesium saturation contents (>40%). The calcium:magnesium ratio (Ca:Mg) serves as a guide to the influence of magnesium. Generally calcium dominated soils (Ca:Mg >2) are well structured, allowing for optimal soil water storage. ESP is less critical in calcium-dominated soils particularly those containing calcium carbonate throughout the profile because they are usually well structured. The Ca:Mg ratios less than 0.5 in clay subsoils tend to be associated with coarser structure, making conditions difficult for the extraction of soil water by plants.

CEC (m.equiv.100g-1) CEC (m.equiv.100g-1) 0 20406080 0 20406080 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg BUg 1AD 6AD1 6AD2 6AD3 Figure 27. Mean CEC for the cracking clays Figure 28. Mean CEC for the alluvial duplex soils

CEC (m.equiv.100g-1) CEC (m.equiv.100g-1) 0 20406080 0 20406080 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 29. Mean CEC for the Tertiary Figure 30. Mean CEC for the miscellaneous sediment duplex soils soils

Mean Ca:Mg ratios for the soil groups are shown in Figures 31 to 34. Only soils within three groups, thin surfaced 6AD, TsD and TsUf, have ratios less than 0.5. These soils are also highly sodic in the subsoil.

Ca:Mg Ratio Ca:Mg Ratio 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0.01.02.03.04.05.06.0 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg BUg 1AD 6AD1 6AD2 6AD3 Figure 31. Mean Ca:Mg for the cracking Figure 32. Mean Ca:Mg for the alluvial clays duplex soils

Ca:Mg Ratio Ca:Mg Ratio 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 33. Mean Ca:Mg for the Tertiary Figure 34. Mean Ca:Mg for the sediment duplex soils miscellaneous soils Clay activity ratio The clay activity ratio (CAR) is the CEC per gram of clay (m.eqiv.g.clay-1). As CEC is usually dependent on clay content and the type of clay, CAR is often used as an indication of clay mineralogy where organic matter is not contributing to the CEC (Shields and Williams 1991). The clay mineralogy indicated by various levels of CAR is shown in Table 17.

Table 17. Relationship of clay activity ratio to clay mineralogy Clay activity ratio Clay mineralogy* <0.20 kaolinite 0.20-0.35 kaolinite and illite 0.35-0.55 mixed mineralogy 0.55-0.75 mixed mineralogy with a high proportion of montmorillonite 0.75-0.95 dominantly montmorillonite >0.95 montmorillonite plus feldspars and/or CEC from other than the clay fraction * Department of Natural Resources (1997)

The average CAR values for the soil groups are shown in Figures 35 to 38. The results show the majority of the soils have a mixed mineralogy with a high proportion of montmorillonite. However, TsD with moderately thick A horizons, TsGn and TsUc have a lower CAR indicating a lower proportion of montmorillonite. The BUg soil has a high CAR indicating a high montmorillonite clay fraction, typical of cracking clays on basalt. McDonald and Baker (1986) discussed the range of CAR on similar soils and commented that mineralogy correlates with the age of the parent material.

Clay Activity Ratio Clay Activity Ratio 0.00 0.25 0.50 0.75 1.00 1.25 1.50 0.00 0.25 0.50 0.75 1.00 1.25 1.50 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg BUg 1AD 6AD1 6AD2 6AD3 Figure 35. Mean CAR for the cracking clays Figure 36. Mean CAR for the alluvial duplex soils

Clay Activity Ratio Clay Activity Ratio 0.00 0.25 0.50 0.75 1.00 1.25 1.50 0.00 0.25 0.50 0.75 1.00 1.25 1.50 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 37. Mean CAR for the Tertiary Figure 38. Mean CAR for the miscellaneous sediment duplex soils soils Plant available water capacity Plant available water capacity (PAWC) is a measure of how much water a soil can supply to plants from a profile of nominated depth. PAWC is the amount of water between field capacity and permanent wilting point in a soil, measured in millimetres. Field capacity is the amount of water held in the soil when the soil is fully wet. Permanent wilting point occurs when the tension of water held by the soil becomes too great for the plant to extract further water, so that, below this point the plant begins to die.

Plant growth suffers well before permanent wilting point. In optimal irrigation conditions, water supply is recommended at levels greater than 80% of PAWC to prevent problems with water stress (PG Muller pers. comm.) The plant available water capacity estimation routine (PAWCER) model (Littleboy 1998) determined the PAWC of the soils. The model requires inputs of soil moisture at 1500 kPa (wilting point), particle size analysis, rock percentage and depth increments.

Effective rooting depth is taken to the depth of optimal water extraction by plant roots and has been determined by the depth to: • relatively impermeable clay or rock; • saline layers where EC >0.9 dSm-1 and or chloride > 600 mgkg-1; • sodicity layers where ESP >15 in montmorillonitic soils (CAR>0.55) or ESP >6 in other soils(if CEC > 6 meq.100g-1); • acid layers where pH <5.5; and • magnesium dominant clays (Ca: Mg <0.5).

In cases where none of the above limitations are encountered, effective rooting depth has been estimated at 1.5 m. The estimated effective rooting depth and soil profile PAWC determined by PAWCER for all analysed soils are shown in Table 18.

The cracking clays have the highest PAWC of the soils. However, in 6AUg-10, TsUg-7 and TsUgg-2, there is variation in effective rooting depth causing some profiles to have moderate and moderately high PAWC totals. The alluvial and Tertiary sediment duplex soils generally have moderate to high PAWC. The soils with low PAWC are 1ADd-3, 6ADb-1, 6ADy-3, TsDb and TsDr-1. The 1ADd-4 soil has a variable PAWC ranging from low to moderate, while 1ADb-7 has a high PAWC. Within the miscellaneous group, TsGn and TsUc soils have PAWC ranging from moderate to high. The 6AUf and TsUf soils have a low PAWC range.

Dispersion ratio

The dispersion ratio (R1) is a measurement to determine the soil’s ability to disperse under wet conditions. According to Baker and Eldershaw (1993), the dispersion ratio is determined by: %(silt + clay)dispersed R = 1 %total(silt + clay)

Dispersion ratios for the soil groups are shown in Table 19. The majority of soils in the area have a low tendency to disperse at the surface. However, three alluvial duplex soils and the Tertiary non-cracking clays have a moderate dispersion rating at the surface. Most of the soils are rated as having a high tendency to disperse at depths of 0.9 m with exceptions being the TsGn and the moderately thick surfaced 6AD soils.

Table 18. Effective rooting depths and plant available water capacity of the soils analysed Soil type Effective rooting depth PAWC (mm) PAWC rating* 1ADb-7 1.0 107 high 1ADd-3 0.1-0.3 9-43 low 1ADd-4 0.1-0.3 18-52 very low to moderate 1AUg-9 1.2 110 high 1AUg-12 1.2 159 very high 1AUg-13 0.7 123 high 1AUg-16 0.9 109 high 6ADb-1 0.2 38-42 moderate 6ADb-2 0.9 89 moderately high 6Adr 0.9 93 moderately high 6ADy-3 0.2-0.4 26-42 low 6ADy-6 1.5 90 moderately high 6AUf-3 0.3 43 low 6AUf-4 0.2 36 low 6AUg-4 1.5 178 very high 6AUg-5 1.4 175 very high 6AUg-6 0.6-0.9 103-135 high 6AUg-7 1.5 174 very high 6AUg-8 0.6 92 moderately high 6AUg-10 0.3-0.6 55–98 moderately high 6AUg-12 0.6 120 high BUg-2 0.8 140 high TsDb 0.2 30-36 low TsDr-1 0.2 30 low TsDy-1 0.2-0.5 38-77 moderately high TsDy-8 1.5 95 moderately high TsGn-2 1.5 76–100 moderately high to high TsGn-3 1.5 89 moderately high TsGn-4 1.5 101 high TsGn-5 1.1-1.5 82-99 moderately high TsGn-6 1.5 92-114 moderately high to high TsGn-8 1.2 92 moderately high TsGn-9 1.5 94 moderately high TsUc-2 1.5 88 moderately high TsUf-1 0.6 76 moderately high TsUf-3 0.2 34 low TsUf-6 0.2 33 low TsUg-7 0.3-0.9 55-127 moderate to high TsUgg-2 0.3-1.1 61-159 moderate to high * Furrow irrigation ratings as follows: • very high - PAWC >150 mm • high – PAWC 100-150 mm • moderately high – PAWC 75-100 mm • moderate – PAWC 50-75 mm • low – PAWC 25-50 mm • very low – PAWC <25 mm

Table 19. Mean dispersion ratios for soil subgroups. Mean dispersion ration Soil group Depth 0-0.1 m 0.2-0.3 m 0.5-0.6 m 0.8-0.9 m Cracking clays 1AUg 0.47 0.63 0.72 0.88 6AUg 0.53 0.66 0.78 0.80 TsUg 0.56 0.71 0.84 0.85 Alluvial duplex soils 1AD 0.70 0.70 0.80 0.80 6AD1 0.62 0.62 0.77 0.89 6AD2 0.60 0.62 0.77 0.89 6AD3 0.30 0.50 0.70 0.50 Tertiary sediment duplex soils TsD1 0.42 0.75 0.77 0.80 TsD2 0.30 0.50 0.80 0.90 TsD3 0.43 0.74 0.82 0.73 Miscellaneous soils 6AUf 0.57 0.54 0.78 0.92 TsUf 0.64 0.69 0.89 0.99 TsGn 0.50 0.49 0.55 0.70 Green values represent low tendency for dispersion (<0.6) Blue values represent moderate tendency for dispersion (0.6–0.8) Red values represent high tendency for dispersion (>0.8) (Baker and Eldershaw 1993)

Particle size distribution Particle size distribution refers to the proportions of solid particles within the standard ranges. The soil particle and their size ranges are: • clay (less than 0.002 mm); • silt (0.002 to 0.02 mm); • fine sand (0.02 to 0.2 mm); and • coarse sand (0.2 to 2 mm).

The fine and coarse sand components have been combined in the following discussion. The mean clay percentage for the soil groups is shown in Figures 39 to 42.

Clay % Clay % 0 25 50 75 100 0 25 50 75 100 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg BUg 1AD 6AD1 6AD2 6AD3 Figure 39. Mean clay percentage for the Figure 40. Mean clay percentage for the cracking clays alluvial duplex soils

Clay % Clay % 0255075100 0255075100 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 41. Mean clay percentage for the Figure 42. Mean clay percentage for the Tertiary sediment duplex soils miscellaneous soils The cracking clays show the highest clay percentage of the analysed soils, being in excess of 45% (equating to medium clay and heavier). The BUg soil has a clay percentage of 71-75% (heavy clay) in the upper 0.6m of the profile decreasing to 47% at 0.9 m depth, immediately above weathering basalt. There is a marked increase in clay percentage between the A and B horizons of the duplex soils. Within the B horizon of the duplex soils, clay percentages range from 25 to 40% (sandy clay loam to light clay). The TsUc group has the lowest clay percentage throughout the soil profile.

Sand percentages for the duplex soils are shown in Figure 43 and 44. Generally the thicker A horizon soils have a higher sand content in the surface and subsoil. Soils in the higher alluvial duplex and Tertiary sediment duplex groups have a higher sand content compared to those in the lower alluvial duplex groups. Soils in the lower alluvial group have a higher silt content compared to the other soils, as shown in Table 20. Silt content appears to be related to the age of the soils, with the more recent soils having higher silt contents. Within the higher alluvial duplex soils, soils with thin A horizons have a higher silt content compared to the soils with thicker A horizons.

Sand % Sand % 0 25 50 75 100 0255075100 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AD 6AD1 6AD2 6AD3 TsD1 TsD2 TsD3 Figure 43. Mean sand percentage for the Figure 44. Mean sand percentage for the alluvial duplex soils Tertiary sediment duplex soils

Particle size distribution is a major determinant of pore size distribution (Baker and Eldershaw 1993). For surface horizons that have a near equal mixture of coarse sand/fine sand/silt/clay or a high silt and fine sand component, the finer particles will pack into pores created by the larger particles, reducing soil pore size and creating conditions that inhibit plant root development (in low organic matter situations). Water infiltration is also reduced. With this condition, known as surface crusting, soils set quite hard and require careful management. Three soils (1AUg-16, 1ADd-4 and 6ADb-4) show potential for surface crusting. Cultivation of these soils can exacerbate surface crusting and hardsetting caused by a decrease in organic carbon (from cropping) and by promoting mixing (from tillage).

Table 20. Average silt percentages for the analysed soils. Soil Group Silt percentage Depth 0-0.1 m 0.2-0.3 m 0.5-0.6 m 0.8-0.9 m Cracking clays 1AUg 22 18 20 16 6AUg 16 16 16 16 TsUg 10 10 9 10 BUg 10 10 10 10 Alluvial duplex 1A 21 15 15 14 6AD1 12 10 11 11 6AD2 3 2 2 4 6AD3 1 1 1 1 Tertiary sediment duplex TsD1 6 7 7 6 TsD2 7 5 3 5 TsD3 5 3 3 2 Miscellaneous 6AUf 10 10 10 10 TsUf 9 9 9 7 TsGn 4 3 3 3 TsUc 2 2 4 2

Soil nutrients Selected surface fertility data are shown in Table 21. The ratings used to interpret the levels of nutrients are shown in Appendix 2.

Phosphorus The phosphorus data come from two methods of analysis. Total phosphorus is measured on profile samples using x-ray fluorescence. Mean total phosphorus down the profile is shown in Figures 45 to 48. Available phosphorus is determined on surface samples by acid and/or bicarbonate extraction, which measures the labile phosphorus in the soil. Within this survey, bicarbonate extraction was used which identifies only a small fraction of the total amount of phosphorus in the soil. Availability is dependent on the interaction of mineral forms of phosphorus in the soil with the soil solution; pH plays an important part in this. Acid extractable methods are used where pH is less than 7, but gives similar information to the bicarbonate methods for pH greater than 7. Available bicarbonate extractable phosphorus of the surface soil is shown in Table 21.

Table 21. Mean surface fertility data (0-0.1 m depth) Soil type Extractable nutrient Organic Total Carbon carbon nitrogen nitrogen Phosphorus1 Potassium Copper Zinc2 (%) (%) ratio (mg kg-1) (meq 100g-1) (mg kg-1) (mg kg-1) 1ADb-7 42 0.6 1.2 0.80 1.0 0.08 13 1ADd-3 56 0.7 1.1 0.60 1.1 0.09 12 1ADd-4 90 1.2 1.2 0.80 1.7 0.12 14 1AUg12 14 0.9 1.6 0.40 0.9 0.09 10 1AUg13 43 1.3 1.4 0.50 1.6 0.16 10 1AUg-16 55 0.6 1.6 0.60 1.1 0.09 12 6ADb-1 11 0.3 0.9 0.65 0.7 0.06 13 6ADb-2 7 0.3 0.9 0.30 0.7 0.06 11 6ADr 40 1.1 1.3 0.90 1.0 0.09 11 6ADy-3 14 0.4 0.5 0.30 0.7 0.04 17 6ADy-6 21 0.2 0.2 0.50 0.6 0.04 15 6AUf-3 6 0.3 0.7 0.30 0.5 0.06 9 6AUf-4 12 0.4 1.3 0.35 0.7 0.07 10 6AUg-5 13 1.0 1.4 0.40 1.3 0.08 16 6AUg-6 14 0.7 1.4 0.45 1.2 0.11 11 6AUg-8 5 0.7 1.2 0.60 0.6 0.09 6 6AUg-10 11 0.5 1.4 0.45 0.8 0.09 9 6AUg-12 13 0.9 1.5 0.45 0.9 0.09 9 TsDb 20 0.5 1.2 0.65 1.1 0.08 14 TsDr-1 16 0.3 0.6 1.40 0.9 0.04 23 TsDy-1 16 0.4 0.7 0.50 0.9 0.05 18 TsDy-8 5 0.2 0.2 0.30 0.4 0.04 11 TsGn-2 7 0.2 0.4 0.30 0.4 0.03 14 TsGn-3 35 0.3 0.4 0.70 1.0 0.05 19 TsGn-4 14 0.4 0.7 0.70 0.6 0.04 14 TsGn-5 10 0.3 0.6 0.50 0.6 0.05 14 TsGn-6 13 0.4 0.8 0.65 0.8 0.06 14 TsGn-8 11 0.4 0.5 0.40 0.8 0.05 16 TsGn-9 6 0.2 0.3 0.20 0.4 0.03 12 TsUc-2 35 0.4 0.4 1.30 0.8 0.05 16 TsUf-1 31 0.5 1.0 0.60 0.3 0.12 3 TsUf-3 9 0.2 0.9 0.70 0.9 0.06 15 TsUf-6 5 0.2 0.7 0.20 0.6 0.04 16 TsUf-6 Ug-9 7 0.5 1.0 0.40 1.0 0.11 9 TsUg-7 12 0.4 1.1 0.38 1.1 0.10 11 TsUgg-2 23 0.8 1.4 0.55 1.4 0.10 14 Green values represent low ratings Blue values represent moderate ratings Red values represent high ratings 1 Bicarbonate Phosphorus 2 Adjusted for pH. Ratings provided by Bruce and Rayment (1982) and Baker and Eldershaw (1993).

Total Phosphorus (%) Total Phosphorus (% 0.00 0.02 0.04 0.06 0.08 0.10 0.00 0.02 0.04 0.06 0.08 0.10 0.0 0.0

0.3 0.3 Note : No basaltic results

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg 1AD 6AD1 6AD2 6AD3 Figure 45. Mean total phosphorus for the Figure 46. Mean total phosphorus for the cracking clays alluvial duplex soils

Total Phosphorus (%) Total Phosphorus (%) 0.00 0.02 0.04 0.06 0.08 0.10 0.00 0.02 0.04 0.06 0.08 0.10 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 6AUf TsUf TsGn TsUc TsD1 TsD2 TsD3 Figure 47. Mean total phosphorus for the Figure 48. Mean total phosphorus for the Tertiary sediment duplex soils miscellaneous soils

Most Australian soils have low phosphorus levels, apart from recent alluvial soils. This is the pattern within the study area. Available phosphorus is high in surface samples of the recent alluvial soils except for 1AUg-12, which has a low rating. The higher alluvial duplex soils with a thin surface have moderate total phosphorus in the surface, although the moderately thick and thick surface duplex soils have low levels. The duplex and miscellaneous soils on Tertiary sediments have variable phosphorus levels. Total phosphorus levels are moderate at the surface for the TsGn, TsUg, TsUf, TsUc and Ts shallow duplex soils. The moderately thick and thick A horizon duplex soils have low surface readings. Under irrigation most of the soils will require phosphorus fertiliser, depending on crop needs.

Soils with high available phosphorus should require little phosphorus fertiliser, particularly if there are also high to moderate total phosphorus levels throughout the soil profile, as in the lower alluvial soils. Where removal of nutrients occurs through harvesting hay or fodder, replacement levels of phosphorus should be applied particularly in low phosphorus soils. The importance of phosphorus was demonstrated early in the development of the EIA. For example, phosphorus was not applied to irrigated cotton, but early crops became phosphorus deficient, especially on BUg and TsUg soils.

Potassium Mean total potassium of soil groups is shown in Figures 49 to 52 and values for extractable potassium are found in Table 21.

Total Potassium (%) Total Potassium (%) 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 0.0 0.0

0.3 Note : 0.3 No basaltic 0.6 results 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg 1AD 6AD1 6AD2 6AD3 Figure 49. Mean total potassium for the Figure 50. Mean total potassium for the cracking clays alluvial duplex soils

Total Potassium (%) Total Potassium (%) 0.0 0.5 1.0 1.5 2.0 0.00.51.01.52.0 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 51. Mean total potassium for the Figure 52. Mean total potassium for the Tertiary sediment duplex soils miscellaneous soils

Total potassium is often used as a guide to the age of alluvial sediments i.e. soils with the higher total potassium being the youngest due to the higher levels of little weathered or unweathered minerals. Within the study area, the lower alluvial soils have high total potassium. The higher alluvial soils have moderate levels of total potassium, with the thick A horizon duplex soils having high levels below 0.9 m. The Tertiary sediments have consistently low total potassium, with the non-cracking clay group having very low levels.

The levels of extractable potassium in the surface show some variability across landscape groups, however, some trends are clear. The recent alluvial soils and the cracking clays of the higher alluvium all contain high levels. Most of the other higher alluvial soils have moderate levels, the only exception being 6ADy-6. The Tertiary sediments show the most variability, with TsDb, TsUf-1 and TsUgg-2 having high extractable potassium in the surface with the TsDy-8, TsGn-2, TsGn-9, TsUf-3 and TsUf-6 having low levels. Potassium fertiliser may be required on some of the well-drained Tertiary sediments soils as reserves are possibly low and little can be taken up from the subsoil. Where high removal of nutrients occurs as in fodder and hay crops, potassium may need to be added except on those soils with very high levels of potassium.

Carbon and nitrogen It is desirable to promote a high organic carbon level in the surface soil, as it is a measure of the soils organic matter content. Organic matter in surface soils influences water-holding capacity, cation exchange capacity, and also relates to soil aggregation through the influence of some organic substances. It also acts as a store of soil carbon, nitrogen, phosphorus and sulfur (Baker and Eldershaw 1993) and contributes to CEC. The organic carbon percentages for the soils are shown in Table 21. Two soils, 1ADd-14 and 1AUg-13, have moderate organic carbon levels, while all the others have low levels. All soils under cultivation suffer some decline in organic matter content, which decreases to a new equilibrium level. Instances of decline in organic carbon after cultivation are given in Baker and Eldershaw (1993). Part of the structural degradation induced by cultivation may relate to reduced organic matter and its influence on maintaining the grade of structure.

The organic carbon content under cultivation can be maintained as high as possible through protection of the soil surface from soil erosion, avoiding excessive tillage, and maintaining good crop growth through supply of adequate nutrients and water. Levels of organic matter can be increased through addition of plant materials or manure, and no-till management systems.

Total nitrogen levels are shown in Table 21. All soils except, for 1AUg-13, have low levels. Under irrigation, nitrogen fertilisers will be required for most crops for optimum growth. On the well-drained highly permeable soils such as TsGn, TsUc and thick surface duplex soils, management must ensure that nitrogen fertiliser are not applied excessively, beyond what the crop can use and what the soil can retain. This will help to avoid leaching of nitrates into groundwater or streams. The carbon: nitrogen ratio of a soil provides some indication of a soil’s ability to mineralise nitrogen. Carbon: nitrogen (C:N) ratios are shown in Table 21. C:N ratios should be 10 to 12 in order to avoid mineralisation problems where soil nitrogen is tied up by soil microbes decomposing excess organic matter. Low values in 6AUg-8 and TsUf-1 soils are due to high nitrogen levels. High C:N ratios indicate some problem may be encountered with mineralisation of nitrogen, which may occur in 6ADy-3, 6ADy-6, 6AUg-5, TsDr-1, TsDy-1, TsGn-3, TsGn8, TsUc-2, TsUf-3, and TsUf-6 soils.

Sulfur Sulfur levels were determined by measuring total sulfur. According to Baker and Eldershaw (1993) sulphates are readily dissolved and can be leached out in well-drained soils, resulting in seasonally variable sulfur levels. In alkaline clay soils, sulphates generally crystallise to form gypsum in the subsoil (Baker and Eldershaw 1993). Mean total sulfur of soil groups is shown in Figures 53 to 56. Total sulfur range from very low to high (0.001% to 0.054%).

Total Sulfur (%) Total Sulfur (%) 0.000 0.025 0.050 0.075 0.100 0.000 0.025 0.050 0.075 0.100 0.0 0.0

Note : No bas altic res ults 0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 1AUg 6AUg TsUg 1AD 6AD1 6AD2 6AD3 Figure 53. Mean total sulfur for the Figure 54. Mean total sulfur for the alluvial cracking clays duplex soils

Total Sulfur (%) Total Sulfur (%) 0.000 0.025 0.050 0.075 0.100 0.000 0.025 0.050 0.075 0.100 0.0 0.0

0.3 0.3

0.6 0.6

0.9 0.9 Depth (m) Depth (m)

1.2 1.2

1.5 1.5 TsD1 TsD2 TsD3 6AUf TsUf TsGn TsUc Figure 55. Mean total sulfur for the Tertiary Figure 56. Mean total sulfur for the sediment duplex soils miscellaneous soils

Micronutrients (copper and zinc) Micronutrients are usually strongly bound in a soil and the soil solution contains low concentrations so that it can only supply a very small part of the crop seasonal requirements (Baker and Eldershaw, 1993). The DTPA method was used for the analysis of micronutrients, namely copper, zinc, iron and manganese. The availability of a specific nutrient is not provided and critical ranges for plant growth are poorly defined; the rating for copper and zinc levels provided by Baker and Eldershaw (1993) are a general guide only.

Surface levels for copper and zinc are shown in Table 21. The majority of the soils have moderate levels according to Baker and Eldershaw (1993). However, two soils, 6ADy-6 and TsDy-8, show low levels of copper. These two soils have thick permeable A horizons and the low copper levels may be attributed to this. The cracking clays and non-cracking clays, except for 1AUg-16 and TsUf-3, have low levels of zinc. This is due to cracking clays having an alkaline surface and zinc levels generally decreasing with rising pH.

The duplex soils, particularly the 1A group, have moderate levels of zinc, except for 6ADb-2, 6ADy-3 and TsDy-8. McDonald and Baker (1986) also observed similar and higher zinc levels in the 1A duplex soils. Zinc deficiency may occur in the strongly alkaline soils and application of zinc fertiliser may be beneficial for plant grow.

8.0 LAND USE

8.1 Land use prior to irrigation development

The principal rural industries in the survey area before the development of irrigation were beef cattle raising and dryland farming. Relatively little clearing was carried out until the imminent development of the irrigation scheme. A dairy operated on portions 1 and 2, parish of Weemah and also grazed the rifle range reserve (Reserve R71). The Emerald Rural Training School was established on portion 49, parish of Weemah. Most of that area was cleared. Dryland cropping was conducted mainly on the cracking clay soils, chiefly in landscape units 6A and B. Cropping was also conducted on landscape unit Ts on cracking clay and other soils. Irrigation had been practised on a variety of soils over the area, which included duplex soils 1ADb-1, and 1ADb-9 for dairy pasture and forage; BUg-2; and 1AUf-6, 1AUg-9 and 1ADd-4 near the McCosker weir. In 1965 the Queensland Water Resources Commission established Pilot Farm No 2. The site was representative of the principal soils of landscape unit Ts. Experience with cropping on the pilot farm contributed a great deal to understanding the behaviour of the soils under irrigation. The Department of Primary Industries ran dryland and irrigated agronomic trials on BUg-2 soils around GR 196 971 (McCosker lease block).

8.2 Land use after irrigation development

Cotton has become the predominant irrigated summer crop (26,000 ha in 1999) across the whole EIA. Other summer crops are maize, sunflower and sorghum. Irrigated winter cropping is minimal and consists mainly of wheat. The climate of Emerald and reliability of water have enabled the establishment of a substantial horticultural industry in Emerald. Citrus (mandarins and oranges) and table grapes are the main horticultural crops within the area. Other horticultural crops include avocado, mango and cucurbits (pumpkin and zucchini). Recent advances in trickle tape technology have led to development of more land for horticultural production, due to improvement in water use efficiency.

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